Image coding method, image decoding method, image coding apparatus, and image decoding apparatus

ABSTRACT

An image coding method includes: deriving a candidate for a motion vector of a current block from a co-located motion vector; adding the candidate to a list; selecting the motion vector of the current block from the list; and coding the current block, wherein the deriving includes: deriving the candidate by a first derivation scheme in the case of determining that each of a current reference picture and a co-located reference picture is a long-term reference picture; and deriving the candidate by a second derivation scheme in the case of determining that each of the current reference picture and the co-located reference picture is a short-term reference picture.

FIELD

One or more exemplary embodiments disclosed herein relate generally toan image coding method of coding each of blocks of pictures.

BACKGROUND

A technique relating to an image coding method of coding each of blocksof pictures is described in Non Patent Literature (NPL) 1.

CITATION LIST Non Patent Literature

-   [NPL 1]-   ISO/IEC 14496-10—MPEG-4 Part 10, Advanced Video Coding

SUMMARY Technical Problem

However, there are cases where the conventional image coding methodcannot achieve sufficiently high coding efficiency.

In view of this, one non-limiting and exemplary embodiment provides animage coding method that can improve coding efficiency in image coding.

Solution to Problem

In one general aspect, the techniques disclosed here feature an imagecoding method of coding each of blocks of pictures, the image codingmethod including: deriving a candidate for a motion vector of a currentblock to be coded, from a motion vector of a co-located block which is ablock included in a picture different from a picture that includes thecurrent block; adding the derived candidate to a list; selecting themotion vector of the current block from the list to which the candidateis added; and coding the current block using the selected motion vectorand a reference picture of the current block, wherein the derivingincludes: determining whether the reference picture of the current blockis a long-term reference picture or a short-term reference picture, andwhether a reference picture of the co-located block is a long-termreference picture or a short-term reference picture; deriving thecandidate from the motion vector of the co-located block by a firstderivation scheme that does not involve scaling based on a temporaldistance, in the case of determining that each of the reference pictureof the current block and the reference picture of the co-located blockis a long-term reference picture; and deriving the candidate from themotion vector of the co-located block by a second derivation scheme thatinvolves scaling based on a temporal distance, in the case ofdetermining that each of the reference picture of the current block andthe reference picture of the co-located block is a short-term referencepicture.

These general and specific aspects may be implemented using a system, anapparatus, an integrated circuit, a computer program, or anon-transitory computer-readable recording medium such as a CD-ROM, orany combination of systems, apparatuses, methods, integrated circuits,computer programs, and recording media.

Additional benefits and advantages of the disclosed embodiments will beapparent from the Specification and Drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the Specification and Drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

Advantageous Effects

One or more exemplary embodiments or features disclosed herein providean image coding method that can improve coding efficiency in imagecoding.

BRIEF DESCRIPTION OF DRAWINGS

These and other advantages and features will become apparent from thefollowing description thereof taken in conjunction with the accompanyingDrawings, by way of non-limiting examples of embodiments of the presentdisclosure.

FIG. 1 is a flowchart showing an operation of an image coding apparatusaccording to a reference example.

FIG. 2 is a flowchart showing an operation of an image decodingapparatus according to the reference example.

FIG. 3 is a flowchart showing details of a derivation process accordingto the reference example.

FIG. 4 is a diagram for explaining a co-located block according to thereference example.

FIG. 5 is a block diagram of an image coding apparatus according toEmbodiment 1.

FIG. 6 is a block diagram of an image decoding apparatus according toEmbodiment 1.

FIG. 7 is a flowchart showing an operation of the image coding apparatusaccording to Embodiment 1.

FIG. 8 is a flowchart showing an operation of the image decodingapparatus according to Embodiment 1.

FIG. 9 is a flowchart showing details of a derivation process accordingto Embodiment 1.

FIG. 10 is a flowchart showing details of a derivation process accordingto Embodiment 2.

FIG. 11 is a diagram for explaining a co-located block according toEmbodiment 2.

FIG. 12 is a flowchart showing details of a derivation process accordingto Embodiment 3.

FIG. 13A is a block diagram of an image coding apparatus according toEmbodiment 4.

FIG. 13B is a flowchart showing an operation of the image codingapparatus according to Embodiment 4.

FIG. 14A is a block diagram of an image decoding apparatus according toEmbodiment 4.

FIG. 14B is a flowchart showing an operation of the image decodingapparatus according to Embodiment 4.

FIG. 15A is a diagram showing a first example of a storage location of aparameter indicating a reference picture classification.

FIG. 15B is a diagram showing a second example of the storage locationof the parameter indicating the reference picture classification.

FIG. 15C is a diagram showing a third example of the storage location ofthe parameter indicating the reference picture classification.

FIG. 16 is a diagram showing an example of a storage location of aparameter indicating a prediction mode.

FIG. 17 illustrates an overall configuration of a content providingsystem for implementing content distribution services.

FIG. 18 illustrates an overall configuration of a digital broadcastingsystem.

FIG. 19 is a block diagram illustrating an example of a configuration ofa television.

FIG. 20 is a block diagram illustrating an example of a configuration ofan information reproducing/recording unit that reads and writesinformation from or on a recording medium that is an optical disk.

FIG. 21 shows an example of a configuration of a recording medium thatis an optical disk.

FIG. 22A shows an example of a cellular phone.

FIG. 22B shows an example of a configuration of the cellular phone.

FIG. 23 shows a structure of multiplexed data.

FIG. 24 schematically illustrates how each of streams is multiplexed inmultiplexed data.

FIG. 25 illustrates how a video stream is stored in a stream of PESpackets in more detail.

FIG. 26 shows a structure of TS packets and source packets in themultiplexed data.

FIG. 27 shows a data structure of a PMT.

FIG. 28 shows an internal structure of multiplexed data information.

FIG. 29 shows an internal structure of stream attribute information.

FIG. 30 shows steps for identifying video data.

FIG. 31 is a block diagram illustrating an example of a configuration ofan integrated circuit for implementing the moving picture coding methodand the moving picture decoding method according to each of Embodiments.

FIG. 32 shows a configuration for switching between driving frequencies.

FIG. 33 shows steps for identifying video data and switching betweendriving frequencies.

FIG. 34 shows an example of a look-up table in which standards of videodata are associated with the driving frequencies.

FIG. 35A shows an example of a configuration for sharing a module of asignal processing unit.

FIG. 35B shows another example of a configuration for sharing a moduleof a signal processing unit.

DESCRIPTION OF EMBODIMENTS

(Underlying Knowledge Forming Basis of the Present Disclosure)

In relation to the image coding method disclosed in the Background Artsection, the inventors have found the following problem. Note that, inthe following description, an image may be any of a moving imagecomposed of a plurality of pictures, a still image composed of onepicture, a part of a picture, and the like.

Image coding schemes in recent years include MPEG-4 AVC/H.264 and HEVC(High Efficiency Video Coding). In these image coding schemes, interprediction using coded reference pictures is available.

Moreover, in these image coding schemes, a reference picture called along-term reference picture may be used. For example, in the case wherea reference picture is retained in a DPB (Decoded Picture Buffer) for along time, the reference picture may be used as a long-term referencepicture.

In HEVC, there is a mode called a merge mode. In the merge mode, amotion vector predictor obtained by predicting a motion vector of acurrent block from a motion vector of an adjacent block or the like isused for coding the current block as the motion vector of the currentblock. That is, in the merge mode, the motion vector predictor istreated as the motion vector of the current block. The motion vectorpredictor and the motion vector of the current block in the merge modeare also referred to as a merge vector.

In HEVC, a temporal motion vector predictor can be used, too. Thetemporal motion vector predictor is derived from a motion vector of aco-located block in a coded co-located picture. Coordinates of theco-located block in the co-located picture correspond to coordinates ofthe current block in the current picture to be coded.

Hereafter, the motion vector of the co-located block is also referred toas a co-located motion vector, and a reference picture of the co-locatedblock is also referred to as a co-located reference picture. Theco-located block is coded using the co-located motion vector and theco-located reference picture. Note that “co-located” may also be writtenas “collocated”.

Likewise, the motion vector of the current block is also referred to asa current motion vector, and a reference picture of the current block isalso referred to as a current reference picture. The current block iscoded using the current motion vector and the current reference picture.

The current block and the co-located block mentioned above are each aprediction unit (PU). The prediction unit is a block of an image, and isdefined as a data unit for prediction. In HEVC, a coding unit (CU) isdefined as a data unit for coding, separately from the prediction unit.The prediction unit is a block in the coding unit. In the followingdescription, the term “block” may be replaced with “prediction unit” or“coding unit”.

The coding unit and the prediction unit are not fixed in size. Forexample, one picture may include a plurality of coding units of varioussizes, and one picture may include a plurality of prediction units ofvarious sizes.

This can cause a situation where a block that exactly matches an area ofthe current block is not defined in the co-located picture. Accordingly,in HEVC, the co-located block is selected from a plurality of blocksincluded in the co-located picture by a predetermined selection method.

The temporal motion vector predictor is generated by scaling the motionvector of the selected co-located block based on a POC (Picture OrderCount) distance. POCs are ordinal numbers assigned to pictures indisplay order. A POC distance corresponds to a temporal distance betweentwo pictures. Scaling based on a POC distance is also referred to asPOC-based scaling. Expression 1 below is an arithmetic expression forperforming POC-based scaling on the motion vector of the co-locatedblock.pmv=(tb/td)×colmv  (Expression 1).

Here, colmv is the motion vector of the co-located block. pmv is thetemporal motion vector predictor derived from the motion vector of theco-located block. tb is a signed POC distance, representing a differencebetween the current picture and the current reference picture. td is asigned POC distance, representing a difference between the co-locatedpicture and the co-located reference picture.

In the case where a valid temporal motion vector predictor is present,the temporal motion vector predictor is inserted into an ordered list ofcurrent motion vector candidates. The motion vector used for coding thecurrent block is selected from the ordered list of current motion vectorcandidates. The selected motion vector is indicated by a parameter in abitstream.

FIG. 1 is a flowchart showing an operation of an image coding apparatusaccording to a reference example. In particular, FIG. 1 shows a processof coding an image by inter prediction.

First, the image coding apparatus classifies each of reference picturesas a short-term reference picture or a long-term reference picture (StepS101). The image coding apparatus writes information indicating theclassification of each of the reference pictures, to a header of thebitstream (Step S102).

Next, the image coding apparatus identifies the current referencepicture (Step S103). The image coding apparatus then derives the currentmotion vector (Step S104). A derivation process will be described indetail later.

Following this, the image coding apparatus generates a prediction block,by performing motion compensation using the current reference pictureand the current motion vector (Step S105).

The image coding apparatus subtracts the prediction block from thecurrent block, to generate a residual block (Step S106). Lastly, theimage coding apparatus codes the residual block, to generate thebitstream including the coded residual block (Step S107).

FIG. 2 is a flowchart showing an operation of an image decodingapparatus according to the reference example. In particular, FIG. 2shows a process of decoding an image by inter prediction.

First, the image decoding apparatus obtains the bitstream, and obtainsthe information indicating the classification of each of the referencepictures by parsing the header of the bitstream (Step S201). The imagedecoding apparatus also obtains the residual block, by parsing thebitstream (Step S202).

Next, the image decoding apparatus identifies the current referencepicture (Step S203). The image decoding apparatus then derives thecurrent motion vector (Step S204). A derivation process will bedescribed in detail later. Following this, the image decoding apparatusgenerates the prediction block, by performing motion compensation usingthe current reference picture and the current motion vector (Step S205).Lastly, the image decoding apparatus adds the prediction block to theresidual block, to generate a reconstructed block (Step S206).

FIG. 3 is a flowchart showing details of the derivation process shown inFIGS. 1 and 2 . The following describes the operation of the imagecoding apparatus. The operation of the image decoding apparatus is thesame as the operation of the image coding apparatus, with “coding” beingreplaced with “decoding”.

First, the image coding apparatus selects the co-located picture (StepS301). Next, the image coding apparatus selects the co-located block inthe co-located picture (Step S302). The image coding apparatus thenidentifies the co-located reference picture and the co-located motionvector (Step S303). After this, the image coding apparatus derives thecurrent motion vector by a derivation scheme that involves POC-basedscaling (Step S304).

FIG. 4 is a diagram for explaining the co-located block used in thederivation process shown in FIG. 3 . The co-located block is selectedfrom a plurality of blocks in the co-located picture.

The co-located picture is different from the current picture thatincludes the current block. For example, the co-located picture is apicture immediately preceding or immediately following the currentpicture in display order. In more detail, for example, the co-locatedpicture is a reference picture listed first in any of two referencepicture lists used for coding of B pictures (bi-predictive coding).

A first block including a sample c0 in the co-located picture is aleading candidate for the co-located block, and is also referred to as aprimary co-located block. A second block including a sample c1 in theco-located picture is a second leading candidate for the co-locatedblock, and is also referred to as a secondary co-located block.

Let (x, y) be coordinates of a top left sample tl in the current block,w be a width of the current block, and h be a height of the currentblock. Coordinates of the sample c0 are (x+w, y+h). Coordinates of thesample c1 are (x+(w/2)−1, y+(h/2)−1).

In the case where the first block is not available, the second block isselected as the co-located block. Examples of the case where the firstblock is not available include the case where the first block is notpresent because the current block is located rightmost or bottommost inthe picture, and the case where the first block is coded by intraprediction.

The following describes a more specific example of the process ofderiving the temporal motion vector predictor as the current motionvector with reference to FIG. 3 again.

First, the image coding apparatus selects the co-located picture (StepS301). Next, the image coding apparatus selects the co-located block(Step S302). In the case where the first block including the sample c0shown in FIG. 4 is available, the first block is selected as theco-located block. In the case where the first block is not available andthe second block including the sample c1 shown in FIG. 4 is available,the second block is selected as the co-located block.

In the case where the available co-located block is selected, the imagecoding apparatus sets the temporal motion vector predictor as available.In the case where the available co-located block is not selected, theimage coding apparatus sets the temporal motion vector predictor as notavailable.

In the case where the temporal motion vector predictor is set asavailable, the image coding apparatus identifies the co-located motionvector as a base motion vector. The image coding apparatus alsoidentifies the co-located reference picture (Step S303).

The image coding apparatus then derives the temporal motion vectorpredictor from the base motion vector by scaling according to Expression1 (Step S304).

Through the process described above, the image coding apparatus and theimage decoding apparatus each derive the temporal motion vectorpredictor as the current motion vector.

There are, however, cases where it is difficult to derive theappropriate current motion vector, depending on the relations betweenthe current picture, the current reference picture, the co-locatedpicture, and the co-located reference picture.

For instance, in the case where the current reference picture is along-term reference picture, there is a possibility that the temporaldistance between the current reference picture and the current pictureis long. In the case where the co-located reference picture is along-term reference picture, there is a possibility that the temporaldistance between the co-located reference picture and the co-locatedpicture is long.

These cases incur a possibility that an extremely large or small currentmotion vector is generated as a result of POC-based scaling. This causesdegradation in prediction accuracy and degradation in coding efficiency.In particular, the extremely large or small current motion vector cannotbe appropriately expressed with a fixed number of bits, leading tosignificant prediction accuracy degradation and coding efficiencydegradation.

An image coding method according to an exemplary embodiment disclosedherein is an image coding method of coding each of blocks of pictures,the image coding method including: deriving a candidate for a motionvector of a current block to be coded, from a motion vector of aco-located block which is a block included in a picture different from apicture that includes the current block; adding the derived candidate toa list; selecting the motion vector of the current block from the listto which the candidate is added; and coding the current block using theselected motion vector and a reference picture of the current block,wherein the deriving includes: determining whether the reference pictureof the current block is a long-term reference picture or a short-termreference picture, and whether a reference picture of the co-locatedblock is a long-term reference picture or a short-term referencepicture; deriving the candidate from the motion vector of the co-locatedblock by a first derivation scheme that does not involve scaling basedon a temporal distance, in the case of determining that each of thereference picture of the current block and the reference picture of theco-located block is a long-term reference picture; and deriving thecandidate from the motion vector of the co-located block by a secondderivation scheme that involves scaling based on a temporal distance, inthe case of determining that each of the reference picture of thecurrent block and the reference picture of the co-located block is ashort-term reference picture.

Thus, the candidate for the current motion vector is appropriatelyderived without being extremely large or small. This contributes toimproved prediction accuracy and improved coding efficiency.

For example, in the deriving: the deriving of the candidate from themotion vector of the co-located block may not be performed in the caseof determining that one of the reference picture of the current blockand the reference picture of the co-located block is a long-termreference picture and the other one of the reference picture of thecurrent block and the reference picture of the co-located block is ashort-term reference picture; and the deriving of the candidate from themotion vector of the co-located block may be performed in the case ofdetermining that each of the reference picture of the current block andthe reference picture of the co-located block is a long-term referencepicture or in the case of determining that each of the reference pictureof the current block and the reference picture of the co-located blockis a short-term reference picture.

Thus, in the case where low prediction accuracy is expected, thecandidate for the current motion vector is not derived from the motionvector of the co-located block. Prediction accuracy degradation can beprevented in this way.

For example, the coding may further include coding informationindicating whether the reference picture of the current block is along-term reference picture or a short-term reference picture, andinformation indicating whether the reference picture of the co-locatedblock is a long-term reference picture or a short-term referencepicture.

Thus, the information indicating, for each reference picture, whetherthe reference picture is a long-term reference picture or a short-termreference picture is provided from the coding side to the decoding side.This enables the coding side and the decoding side to obtain the samedetermination result and perform the same process.

For example, the deriving may include: determining whether the referencepicture of the current block is a long-term reference picture or ashort-term reference picture, using a temporal distance between thereference picture of the current block and the picture that includes thecurrent block; and determining whether the reference picture of theco-located block is a long-term reference picture or a short-termreference picture, using a temporal distance between the referencepicture of the co-located block and the picture that includes theco-located block.

Thus, for each reference picture, whether the reference picture is along-term reference picture or a short-term reference picture is simplyand appropriately determined based on the temporal distance.

For example, the deriving may include determining whether the referencepicture of the co-located block is a long-term reference picture or ashort-term reference picture, in a period during which the co-locatedblock is coded.

Thus, whether the reference picture of the co-located block is along-term reference picture or a short-term reference picture isdetermined more accurately.

For example, the deriving may include determining whether the referencepicture of the co-located block is a long-term reference picture or ashort-term reference picture, in a period during which the current blockis coded.

Thus, information indicating whether the reference picture of theco-located block is a long-term reference picture or a short-termreference picture need not be retained for a long time.

For example, the deriving may include: deriving the motion vector of theco-located block as the candidate, in the case of determining that eachof the reference picture of the current block and the reference pictureof the co-located block is a long-term reference picture; and derivingthe candidate by scaling the motion vector of the co-located block usinga ratio, in the case of determining that each of the reference pictureof the current block and the reference picture of the co-located blockis a short-term reference picture, the ratio being a ratio of a temporaldistance between the reference picture of the current block and thepicture that includes the current block to a temporal distance betweenthe reference picture of the co-located block and the picture thatincludes the co-located block.

Thus, in the case where the two reference pictures are each a long-termreference picture, scaling is omitted, with it being possible to reducecomputation. In the case where the two reference pictures are each ashort-term reference picture, the candidate for the current motionvector is appropriately derived based on the temporal distance.

For example, the deriving may further include, without deriving thecandidate from the co-located block, selecting another co-located blockand deriving the candidate from a motion vector of the other co-locatedblock by the second derivation scheme, in the case of determining thatthe reference picture of the current block is a short-term referencepicture and the reference picture of the co-located block is a long-termreference picture, the other co-located block being coded with referenceto a short-term reference picture.

Thus, the block for deriving the candidate of high prediction accuracyis selected. This contributes to improved prediction accuracy.

Moreover, an image decoding method according to an exemplary embodimentdisclosed herein is an image decoding method of decoding each of blocksof pictures, the image decoding method including: deriving a candidatefor a motion vector of a current block to be decoded, from a motionvector of a co-located block which is a block included in a picturedifferent from a picture that includes the current block; adding thederived candidate to a list; selecting the motion vector of the currentblock from the list to which the candidate is added; and decoding thecurrent block using the selected motion vector and a reference pictureof the current block, wherein the deriving includes: determining whetherthe reference picture of the current block is a long-term referencepicture or a short-term reference picture, and whether a referencepicture of the co-located block is a long-term reference picture or ashort-term reference picture; deriving the candidate from the motionvector of the co-located block by a first derivation scheme that doesnot involve scaling based on a temporal distance, in the case ofdetermining that each of the reference picture of the current block andthe reference picture of the co-located block is a long-term referencepicture; and deriving the candidate from the motion vector of theco-located block by a second derivation scheme that involves scalingbased on a temporal distance, in the case of determining that each ofthe reference picture of the current block and the reference picture ofthe co-located block is a short-term reference picture.

Thus, the candidate for the current motion vector is appropriatelyderived without being extremely large or small. This contributes toimproved prediction accuracy and improved coding efficiency.

For example, in the deriving: the deriving of the candidate from themotion vector of the co-located block may not be performed in the caseof determining that one of the reference picture of the current blockand the reference picture of the co-located block is a long-termreference picture and the other one of the reference picture of thecurrent block and the reference picture of the co-located block is ashort-term reference picture; and the deriving of the candidate from themotion vector of the co-located block may be performed in the case ofdetermining that each of the reference picture of the current block andthe reference picture of the co-located block is a long-term referencepicture or in the case of determining that each of the reference pictureof the current block and the reference picture of the co-located blockis a short-term reference picture.

Thus, in the case where low prediction accuracy is expected, thecandidate for the current motion vector is not derived from the motionvector of the co-located block. Prediction accuracy degradation can beprevented in this way.

For example, the decoding may further include decoding informationindicating whether the reference picture of the current block is along-term reference picture or a short-term reference picture, andinformation indicating whether the reference picture of the co-locatedblock is a long-term reference picture or a short-term referencepicture, wherein the deriving includes: determining whether thereference picture of the current block is a long-term reference pictureor a short-term reference picture, using the information indicatingwhether the reference picture of the current block is a long-termreference picture or a short-term reference picture; and determiningwhether the reference picture of the co-located block is a long-termreference picture or a short-term reference picture, using theinformation indicating whether the reference picture of the co-locatedblock is a long-term reference picture or a short-term referencepicture.

Thus, the information indicating, for each reference picture, whetherthe reference picture is a long-term reference picture or a short-termreference picture is provided from the coding side to the decoding side.This enables the coding side and the decoding side to obtain the samedetermination result and perform the same process.

For example, the deriving may include: determining whether the referencepicture of the current block is a long-term reference picture or ashort-term reference picture, using a temporal distance between thereference picture of the current block and the picture that includes thecurrent block; and determining whether the reference picture of theco-located block is a long-term reference picture or a short-termreference picture, using a temporal distance between the referencepicture of the co-located block and the picture that includes theco-located block.

Thus, for each reference picture, whether the reference picture is along-term reference picture or a short-term reference picture is simplyand appropriately determined based on the temporal distance.

For example, the deriving may include determining whether the referencepicture of the co-located block is a long-term reference picture or ashort-term reference picture, in a period during which the co-locatedblock is decoded.

Thus, whether the reference picture of the co-located block is along-term reference picture or a short-term reference picture isdetermined more accurately.

For example, the deriving may include determining whether the referencepicture of the co-located block is a long-term reference picture or ashort-term reference picture, in a period during which the current blockis decoded.

Thus, information indicating whether the reference picture of theco-located block is a long-term reference picture or a short-termreference picture need not be retained for a long time.

For example, the deriving may include: deriving the motion vector of theco-located block as the candidate, in the case of determining that eachof the reference picture of the current block and the reference pictureof the co-located block is a long-term reference picture; and derivingthe candidate by scaling the motion vector of the co-located block usinga ratio, in the case of determining that each of the reference pictureof the current block and the reference picture of the co-located blockis a short-term reference picture, the ratio being a ratio of a temporaldistance between the reference picture of the current block and thepicture that includes the current block to a temporal distance betweenthe reference picture of the co-located block and the picture thatincludes the co-located block.

Thus, in the case where the two reference pictures are each a long-termreference picture, scaling is omitted, with it being possible to reducecomputation. In the case where the two reference pictures are each ashort-term reference picture, the candidate for the current motionvector is appropriately derived based on the temporal distance.

For example, the deriving may further include, without deriving thecandidate from the co-located block, selecting another co-located blockand deriving the candidate from a motion vector of the other co-locatedblock by the second derivation scheme, in the case of determining thatthe reference picture of the current block is a short-term referencepicture and the reference picture of the co-located block is a long-termreference picture, the other co-located block being decoded withreference to a short-term reference picture.

Thus, the block for deriving the candidate of high prediction accuracyis selected. This contributes to improved prediction accuracy.

Moreover, a content providing method according to an exemplaryembodiment disclosed herein is a content providing method oftransmitting, from a server in which image data coded by the imagecoding method described above is recorded, the image data in response toa request from an external terminal.

These general and specific aspects may be implemented using a system, anapparatus, an integrated circuit, a computer program, or anon-transitory computer-readable recording medium such as a CD-ROM, orany combination of systems, apparatuses, methods, integrated circuits,computer programs, and recording media.

Hereinafter, certain exemplary embodiments are described in greaterdetail with reference to the accompanying Drawings. Each of theexemplary embodiments described below shows a general or specificexample. The numerical values, shapes, materials, structural elements,the arrangement and connection of the structural elements, steps, theprocessing order of the steps etc. shown in the following exemplaryembodiments are mere examples, and therefore do not limit the scope ofthe appended Claims and their equivalents. Therefore, among thestructural elements in the following exemplary embodiments, structuralelements not recited in any one of the independent claims are describedas arbitrary structural elements.

Embodiment 1

FIG. 5 is a block diagram of an image coding apparatus according toEmbodiment 1. An image coding apparatus 500 shown in FIG. 5 codes animage on a block basis, and outputs a bitstream including the codedimage. In detail, the image coding apparatus 500 includes a subtractingunit 501, a transforming unit 502, a quantizing unit 503, an entropycoder 504, an inverse quantizing unit 505, an inverse transforming unit506, an adding unit 507, a block memory 508, a picture memory 509, anintra predicting unit 510, an inter predicting unit 511, and a selectingunit 512.

The subtracting unit 501 subtracts a prediction image from an imageprovided to the image coding apparatus 500, to generate a differentialimage. The transforming unit 502 frequency-transforms the differentialimage generated by the subtracting unit 501, to generate a plurality offrequency coefficients. The quantizing unit 503 quantizes the pluralityof frequency coefficients generated by the transforming unit 502, togenerate a plurality of quantization coefficients. The entropy coder 504codes the plurality of quantization coefficients generated by thequantizing unit 503, to generate a bitstream.

The inverse quantizing unit 505 inverse-quantizes the plurality ofquantization coefficients generated by the quantizing unit 503, torestore the plurality of frequency coefficients. The inversetransforming unit 506 inverse-frequency-transforms the plurality offrequency coefficients restored by the inverse quantizing unit 505, torestore the differential image. The adding unit 507 adds the predictionimage to the differential image restored by the inverse transformingunit 506, to restore (reconstruct) the image. The adding unit 507 storesthe restored image (reconstructed image) in the block memory 508 and thepicture memory 509.

The block memory 508 is a memory for storing the image restored by theadding unit 507, on a block basis. The picture memory 509 is a memoryfor storing the image restored by the adding unit 507, on a picturebasis.

The intra predicting unit 510 performs intra prediction by referencingto the block memory 508. That is, the intra predicting unit 510 predictsa pixel value in a picture from another pixel value in the picture. Theintra predicting unit 510 thus generates the prediction image. The interpredicting unit 511 performs inter prediction by referencing to thepicture memory 509. That is, the inter predicting unit 511 predicts apixel value in a picture from a pixel value in another picture. Theinter predicting unit 511 thus generates the prediction image.

The selecting unit 512 selects any of the prediction image generated bythe intra predicting unit 510 and the prediction image generated by theinter predicting unit 511, and outputs the selected prediction image tothe subtracting unit 501 and the adding unit 507.

Though not shown in FIG. 5 , the image coding apparatus 500 may includea deblocking filtering unit. The deblocking filtering unit may perform adeblocking filtering process on the image restored by the adding unit507, to remove noise near block boundaries. The image coding apparatus500 may also include a controlling unit that controls each process inthe image coding apparatus 500.

FIG. 6 is a block diagram of an image decoding apparatus according tothis embodiment. An image decoding apparatus 600 shown in FIG. 6 obtainsthe bitstream, and decodes the image on a block basis. In detail, theimage decoding apparatus 600 includes an entropy decoder 601, an inversequantizing unit 602, an inverse transforming unit 603, an adding unit604, a block memory 605, a picture memory 606, an intra predicting unit607, an inter predicting unit 608, and a selecting unit 609.

The entropy decoder 601 decodes the coded plurality of quantizationcoefficients included in the bitstream. The inverse quantizing unit 602inverse-quantizes the plurality of quantization coefficients decoded bythe entropy decoder 601, to restore the plurality of frequencycoefficients. The inverse transforming unit 603inverse-frequency-transforms the plurality of frequency coefficientsrestored by the inverse quantizing unit 602, to restore the differentialimage.

The adding unit 604 adds the prediction image to the differential imagerestored by the inverse transforming unit 603, to restore (reconstruct)the image. The adding unit 604 outputs the restored image (reconstructedimage). The adding unit 604 also stores the restored image in the blockmemory 605 and the picture memory 606.

The block memory 605 is a memory for storing the image restored by theadding unit 604, on a block basis. The picture memory 606 is a memoryfor storing the image restored by the adding unit 604, on a picturebasis.

The intra predicting unit 607 performs intra prediction by referencingto the block memory 605. That is, the intra predicting unit 607 predictsa pixel value in a picture from another pixel value in the picture. Theintra predicting unit 607 thus generates the prediction image. The interpredicting unit 608 performs inter prediction by referencing to thepicture memory 606. That is, the inter predicting unit 608 predicts apixel value in a picture from a pixel value in another picture. Theinter predicting unit 608 thus generates the prediction image.

The selecting unit 609 selects any of the prediction image generated bythe intra predicting unit 607 and the prediction image generated by theinter predicting unit 608, and outputs the selected prediction image tothe adding unit 604.

Though not shown in FIG. 6 , the image decoding apparatus 600 mayinclude a deblocking filtering unit. The deblocking filtering unit mayperform a deblocking filtering process on the image restored by theadding unit 604, to remove noise near block boundaries. The imagedecoding apparatus 600 may also include a controlling unit that controlseach process in the image decoding apparatus 600.

The coding process and the decoding process mentioned above areperformed on a coding unit basis. The transformation process, thequantization process, the inverse transformation process, and theinverse quantization process are performed on a transform unit (TU)basis where the transform unit is included in the coding unit. Theprediction process is performed on a prediction unit basis where theprediction unit is included in the coding unit.

FIG. 7 is a flowchart showing an operation of the image coding apparatus500 shown in FIG. 5 . In particular, FIG. 7 shows a process of coding animage by inter prediction.

First, the inter predicting unit 511 classifies each of referencepictures as a short-term reference picture or a long-term referencepicture (Step S701).

The long-term reference picture is a reference picture suitable forlong-term use. The long-term reference picture is defined as a referencepicture for longer use than the short-term reference picture.Accordingly, there is a high possibility that the long-term referencepicture is retained in the picture memory 509 for a long time. Thelong-term reference picture is designated by an absolute POC that doesnot depend on the current picture. Meanwhile, the short-term referencepicture is designated by a POC relative to the current picture.

Next, the entropy coder 504 writes information indicating theclassification of each of the reference pictures, to a header of thebitstream (Step S702). That is, the entropy coder 504 writes informationindicating, for each of the reference pictures, whether the referencepicture is a long-term reference picture or a short-term referencepicture.

Following this, the inter predicting unit 511 identifies the referencepicture of the current block to be coded (to be predicted) (Step S703).The inter predicting unit 511 may identify a reference picture of ablock adjacent to the current block, as the current reference picture.Alternatively, the inter predicting unit 511 may identify the currentreference picture by a predetermined reference index. The interpredicting unit 511 then derives the current motion vector (Step S704).A derivation process will be described in detail later.

The inter predicting unit 511 generates the prediction block, byperforming motion compensation using the current reference picture andthe current motion vector (Step S705). After this, the subtracting unit501 subtracts the prediction block from the current block (originalimage), to generate the residual block (Step S706). Lastly, the entropycoder 504 codes the residual block, to generate the bitstream includingthe residual block (Step S707).

FIG. 8 is a flowchart showing an operation of the image decodingapparatus 600 shown in FIG. 6 . In particular, FIG. 8 shows a process ofdecoding an image by inter prediction.

First, the entropy decoder 601 obtains the bitstream, and obtains theinformation indicating the classification of each of the referencepictures by parsing the header of the bitstream (Step S801). That is,the entropy decoder 601 obtains the information indicating, for each ofthe reference pictures, whether the reference picture is a long-termreference picture or a short-term reference picture. The entropy decoder601 also obtains the residual block, by parsing the bitstream (StepS802).

Next, the inter predicting unit 608 identifies the current referencepicture (Step S803). The inter predicting unit 608 may identify areference picture of a block adjacent to the current block, as thecurrent reference picture. Alternatively, the inter predicting unit 608may identify the current reference picture by a predetermined referenceindex.

Following this, the inter predicting unit 608 derives the current motionvector (Step S804). A derivation process will be described in detaillater. The inter predicting unit 608 then generates the predictionblock, by performing motion compensation using the current referencepicture and the current motion vector (Step S805). Lastly, the addingunit 604 adds the prediction block to the residual block, to generatethe reconstructed block (Step S806).

FIG. 9 is a flowchart showing details of the derivation process shown inFIGS. 7 and 8 . The following mainly describes the operation of theinter predicting unit 511 shown in FIG. 5 . The operation of the interpredicting unit 608 shown in FIG. 6 is the same as the operation of theinter predicting unit 511 shown in FIG. 5 , with “coding” being replacedwith “decoding”.

First, the inter predicting unit 511 selects the co-located picture froma plurality of available reference pictures (Step S901). The pluralityof available reference pictures are coded pictures, and are retained inthe picture memory 509.

Next, the inter predicting unit 511 selects the co-located block in theco-located picture (Step S902). The inter predicting unit 511 thenidentifies the co-located reference picture and the co-located motionvector (Step S903).

Following this, the inter predicting unit 511 determines whether or notany of the current reference picture and the co-located referencepicture is a long-term reference picture (Step S904). In the case ofdetermining that any of the current reference picture and the co-locatedreference picture is a long-term reference picture (Step S904: Yes), theinter predicting unit 511 derives the current motion vector by a firstderivation scheme (Step S905).

The first derivation scheme is a scheme using the co-located motionvector. In more detail, the first derivation scheme is a scheme ofdirectly deriving the co-located motion vector as the current motionvector, without POC-based scaling. The first derivation scheme may be ascheme of deriving the current motion vector by scaling the co-locatedmotion vector at a predetermined ratio.

In the case of determining that none of the current reference pictureand the co-located reference picture is a long-term reference picture(Step S904: No), the inter predicting unit 511 derives the currentmotion vector by a second derivation scheme (Step S906). That is, in thecase of determining that the current reference picture and theco-located reference picture are each a short-term reference picture,the inter predicting unit 511 derives the current motion vector by thesecond derivation scheme.

The second derivation scheme is a scheme using the current referencepicture, the co-located reference picture, and the co-located motionvector. In more detail, the second derivation scheme is a scheme ofderiving the current motion vector by performing POC-based scaling(Expression 1) on the co-located motion vector.

The following describes a more specific example of the process ofderiving the current motion vector with reference to FIG. 9 again. Thederivation process described earlier may be changed as follows.

First, the inter predicting unit 511 selects the co-located picture(Step S901). In more detail, in the case where a slice header parameterslice_type is B and a slice header parameter collocated_from_I0_flag is0, a picture RefPicList1[0] is selected as the co-located picture. Thepicture RefPicList1[0] is a reference picture listed first in an orderedreference picture list RefPicList1.

In the case where the slice header parameter slice_type is not B or inthe case where the slice header parameter collocated_from_I0_flag is not0, a picture RefPicList0[0] is selected as the co-located picture. Thepicture RefPicList0[0] is a reference picture listed first in an orderedreference picture list RefPicList0.

Next, the inter predicting unit 511 selects the co-located block (StepS902). In the case where the first block including the sample c0 shownin FIG. 4 is available, the first block is selected as the co-locatedblock. In the case where the first block is not available and the secondblock including the sample c1 shown in FIG. 4 is available, the secondblock is selected as the co-located block.

In the case where the available co-located block is selected, the interpredicting unit 511 sets the temporal motion vector predictor asavailable. In the case where the available co-located block is notselected, the inter predicting unit 511 sets the temporal motion vectorpredictor as not available.

In the case where the temporal motion vector predictor is set asavailable, the inter predicting unit 511 identifies the co-locatedmotion vector as the base motion vector. The inter predicting unit 511also identifies the co-located reference picture (Step S903). In thecase where the co-located block has a plurality of motion vectors, thatis, in the case where the co-located block is coded using a plurality ofmotion vectors, the inter predicting unit 511 selects the base motionvector according to predetermined priority order.

For example, in the case where the current reference picture is ashort-term reference picture, the inter predicting unit 511 maypreferentially select a motion vector that points to a location in ashort-term reference picture from among the plurality of motion vectors,as the base motion vector.

In detail, in the case where a motion vector that points to a locationin a short-term reference picture is present, the inter predicting unit511 selects the motion vector as the base motion vector. In the casewhere a motion vector that points to a location in a short-termreference picture is not present, the inter predicting unit 511 selectsa motion vector that points to a location in a long-term referencepicture, as the base motion vector.

After this, in the case where any of the current reference picture andthe co-located reference picture is a long-term reference picture (StepS904: Yes), the inter predicting unit 511 derives the base motion vectoras the temporal motion vector predictor (Step S905).

In the case where none of the two reference pictures is a long-termreference picture (Step S904: No), on the other hand, the interpredicting unit 511 derives the temporal motion vector predictor fromthe base motion vector by POC-based scaling (Step S906).

As described above, the temporal motion vector predictor is set asavailable or not available. The inter predicting unit 511 inserts thetemporal motion vector predictor set as available, into an ordered listof current motion vector candidates. The ordered list holds not only thetemporal motion vector predictor but various motion vectors ascandidates.

The inter predicting unit 511 selects one motion vector from the orderedlist, as the current motion vector. Here, the inter predicting unit 511selects a motion vector of highest prediction accuracy for the currentblock or a motion vector that allows the current block to be coded withhighest coding efficiency, from the ordered list. An index correspondingto the selected motion vector is written to the bitstream.

Through the process described above, the current motion vector isappropriately derived from the co-located motion vector, without beingextremely large or small. This contributes to improved predictionaccuracy and improved coding efficiency.

Note that the status of each reference picture as to whether thereference picture is a long-term reference picture or a short-termreference picture may be changed according to time. For example, ashort-term reference picture may later be changed to a long-termreference picture, and a long-term reference picture may later bechanged to a short-term reference picture.

Moreover, the inter predicting unit 511 may determine whether theco-located reference picture is a long-term reference picture or ashort-term reference picture, in a period during which the co-locatedblock is coded. The image coding apparatus 500 may then include anadditional memory for holding the determination result from when theco-located block is coded to when the current block is coded.

In this way, whether the co-located reference picture is a long-termreference picture or a short-term reference picture is determined moreaccurately.

As an alternative, the inter predicting unit 511 may determine whetherthe co-located reference picture is a long-term reference picture or ashort-term reference picture, in a period during which the current blockis coded.

In this way, the information of whether the co-located reference pictureis a long-term reference picture or a short-term reference picture neednot be retained for a long time.

Moreover, the inter predicting unit 511 may determine whether thecurrent reference picture is a long-term reference picture or ashort-term reference picture, using a temporal distance between thecurrent reference picture and the current picture.

As an example, in the case where the temporal distance between thecurrent reference picture and the current picture is more than apredetermined threshold, the inter predicting unit 511 determines thatthe current reference picture is a long-term reference picture. In thecase where the temporal distance is not more than the predeterminedthreshold, the inter predicting unit 511 determines that the currentreference picture is a short-term reference picture.

Likewise, the inter predicting unit 511 may determine whether theco-located reference picture is a long-term reference picture or ashort-term reference picture, using a temporal distance between theco-located reference picture and the co-located picture.

As an example, in the case where the temporal distance between theco-located reference picture and the co-located picture is more than apredetermined threshold, the inter predicting unit 511 determines thatthe co-located reference picture is a long-term reference picture. Inthe case where the temporal distance is not more than the predeterminedthreshold, the inter predicting unit 511 determines that the co-locatedreference picture is a short-term reference picture.

The inter predicting unit 608 in the image decoding apparatus 600 maydetermine, for each reference picture, whether or not the referencepicture is a long-term reference picture or a short-term referencepicture based on a temporal distance, in the same manner as the interpredicting unit 511 in the image coding apparatus 500. In such a case,the information indicating, for each reference picture, whether thereference picture is a long-term reference picture or a short-termreference picture need not be coded.

Regarding each of the other processes described in this embodiment, too,each structural element in the image decoding apparatus 600 performs thesame process as the corresponding structural element in the image codingapparatus 500, as a result of which the image coded with high codingefficiency is appropriately decoded.

The operations described above are also applicable to the otherembodiments. Any of the structures and operations described in thisembodiment may be incorporated in the other embodiments, and any of thestructures and operations described in the other embodiments may beincorporated in this embodiment.

Embodiment 2

An image coding apparatus and an image decoding apparatus according toEmbodiment 2 have the same structures as those in Embodiment 1. Hence,the operations of the image coding apparatus and the image decodingapparatus according to this embodiment are described below, using thestructure of the image coding apparatus 500 shown in FIG. 5 and thestructure of the image decoding apparatus 600 shown in FIG. 6 .

The image coding apparatus 500 according to this embodiment performs theoperation shown in FIG. 7 , as in Embodiment 1. The image decodingapparatus 600 according to this embodiment performs the operation shownin FIG. 8 , as in Embodiment 1. This embodiment differs from Embodiment1 in the current motion vector derivation process. This is described indetail below.

FIG. 10 is a flowchart showing details of the derivation processaccording to this embodiment. The inter predicting unit 511 according tothis embodiment performs the operation shown in FIG. 10 , instead of theoperation shown in FIG. 9 . The following mainly describes the operationof the inter predicting unit 511 shown in FIG. 5 . The operation of theinter predicting unit 608 shown in FIG. 6 is the same as the operationof the inter predicting unit 511 shown in FIG. 5 , with “coding” beingreplaced with “decoding”.

First, the inter predicting unit 511 selects the co-located picture fromthe plurality of available reference pictures (Step S1001). Next, theinter predicting unit 511 selects the co-located block in the co-locatedpicture (Step S1002). The inter predicting unit 511 then identifies theco-located reference picture and the co-located motion vector (StepS1003).

Following this, the inter predicting unit 511 determines whether or notthe current reference picture is a long-term reference picture (StepS1004). In the case of determining that the current reference picture isa long-term reference picture (Step S1004: Yes), the inter predictingunit 511 derives the current motion vector by the first derivationscheme same as in Embodiment 1 (Step S1005).

In the case of determining that the current reference picture is not along-term reference picture (Step S1004: No), the inter predicting unit511 determines whether or not the co-located reference picture is along-term reference picture (Step S1006).

In the case of determining that the co-located reference picture is nota long-term reference picture (Step S1006: No), the inter predictingunit 511 derives the current motion vector by the second derivationscheme same as in Embodiment 1 (Step S1007). That is, in the case ofdetermining that the current reference picture and the co-locatedreference picture are each a short-term reference picture, the interpredicting unit 511 derives the current motion vector by the secondderivation scheme.

In the case of determining that the co-located reference picture is along-term reference picture (Step S1006: Yes), the inter predicting unit511 selects another co-located block in the co-located picture (StepS1008). In the example shown in FIG. 10 , a block coded with referenceto a short-term reference picture is selected as the other co-locatedblock.

After this, the inter predicting unit 511 identifies the co-locatedreference picture and the co-located motion vector corresponding to theother co-located block (Step S1009). The inter predicting unit 511 thenderives the current motion vector by the second derivation scheme thatuses POC-based scaling (Step S1010).

In detail, in the case where the reference picture of the current blockis a short-term reference picture and the reference picture of theco-located block is a long-term reference picture, the inter predictingunit 511 does not derive the current motion vector from the motionvector of the co-located block. The inter predicting unit 511 insteadselects another co-located block coded with reference to a short-termreference picture, and derives the current motion vector from the motionvector of the selected other co-located block.

As an example, in the case where the reference picture of the currentblock is a short-term reference picture and the reference picture of theco-located block is a long-term reference picture, the inter predictingunit 511 searches for a block coded with reference to a short-termreference picture. The inter predicting unit 511 selects the block codedwith reference to the short-term reference picture, as the otherco-located block.

As another example, in the case where the reference picture of thecurrent block is a short-term reference picture and the referencepicture of the co-located block is a long-term reference picture, theinter predicting unit 511 first searches for a block coded withreference to a short-term reference picture.

In the case where the block coded with reference to the short-termreference picture is present, the inter predicting unit 511 selects theblock as the other co-located block. In the case where the block codedwith reference to the short-term reference picture is not present, theinter predicting unit 511 searches for a block coded with reference to along-term reference picture. The inter predicting unit 511 selects theblock coded with reference to the long-term reference picture, as theother co-located block.

For example, the inter predicting unit 511 first selects the first blockshown in FIG. 4 as the co-located block. In the case where the currentreference picture is a short-term reference picture and the co-locatedreference picture is a long-term reference picture, then the interpredicting unit 511 newly selects the second block shown in FIG. 4 asthe co-located block.

In the above-mentioned example, the inter predicting unit 511 may selectthe second block shown in FIG. 4 as the co-located block only in thecase where the reference picture of the second block is a short-termreference picture. The block selected as the co-located block here isnot limited to the second block shown in FIG. 4 , and a block other thanthe second block may be selected as the co-located block.

FIG. 11 is a diagram for explaining the co-located block according tothis embodiment. Samples c0, c1, c2, and c3 in the co-located pictureare shown in FIG. 11 . The samples c0 and c1 in FIG. 11 are equal to thesamples c0 and c1 in FIG. 4 . Not only the second block including thesample c1 but also a third block including the sample c2 or a fourthblock including the sample c3 may be selected as the other co-locatedblock.

Coordinates of the sample c2 are (x+w−1, y+h−1). Coordinates of thesample c3 are (x+1, y+1).

The inter predicting unit 511 determines, for each of the first, second,third, and fourth blocks in this order, whether or not the block isavailable. The inter predicting unit 511 determines the available blockas the final co-located block. Examples of the case where the block isnot available include the case where the block is not present and thecase where the block is coded by intra prediction.

In the case where the current reference picture is a short-termreference picture, the inter predicting unit 511 may determine that ablock coded with reference to a long-term reference picture is notavailable.

Though the above describes the example of the co-located block selectionmethod, the co-located block selection method is not limited to theabove example. A block including a sample other than the samples c0, c1,c2, and c3 may be selected as the co-located block. Besides, thepriority order of the blocks is not limited to the example described inthis embodiment.

The following describes a more specific example of the process ofderiving the current motion vector with reference to FIG. 10 again. Thederivation process described earlier may be changed as follows.

First, the inter predicting unit 511 selects the co-located picture asin Embodiment 1 (Step S1001). Next, the inter predicting unit 511selects the first block including the sample c0 shown in FIG. 11 as theco-located block, and identifies the co-located reference picture (StepsS1002 and S1003).

Following this, the inter predicting unit 511 determines whether or notthe co-located block is available. In the case where the currentreference picture is a short-term reference picture and the co-locatedreference picture is a long-term reference picture, the inter predictingunit 511 determines that the co-located block is not available (StepsS1004 and S1006).

In the case where the co-located block is not available, the interpredicting unit 511 searches for and selects another co-located blockwhich is available (Step S1008). In detail, the inter predicting unit511 selects a block coded with reference to a short-term referencepicture, from among the second block including the sample c1, the thirdblock including the sample c2, and the fourth block including the samplec3 in FIG. 11 . The inter predicting unit 511 then identifies thereference picture of the co-located block (Step S1009).

In the case where the available co-located block is selected, the interpredicting unit 511 sets the temporal motion vector predictor asavailable. In the case where the available co-located block is notselected, the inter predicting unit 511 sets the temporal motion vectorpredictor as not available.

In the case where the temporal motion vector predictor is set asavailable, the inter predicting unit 511 identifies the co-locatedmotion vector as the base motion vector (Steps S1003 and S1009). In thecase where the co-located block has a plurality of motion vectors, thatis, in the case where the co-located block is coded using a plurality ofmotion vectors, the inter predicting unit 511 selects the base motionvector according to predetermined priority order as in Embodiment 1.

In the case where any of the current reference picture and theco-located reference picture is a long-term reference picture (StepS1004: Yes), the inter predicting unit 511 derives the base motionvector as the temporal motion vector predictor (Step S1005).

In the case where none of the current reference picture and theco-located reference picture is a long-term reference picture (StepS1004: No), on the other hand, the inter predicting unit 511 derives thetemporal motion vector predictor from the base motion vector byPOC-based scaling (Steps S1007 and S1010).

In the case where the temporal motion vector predictor is set as notavailable, the inter predicting unit 511 does not derive the temporalmotion vector predictor.

As in Embodiment 1, the inter predicting unit 511 adds the temporalmotion vector predictor set as available, to the list as the candidatefor the current motion vector. The inter predicting unit 511 thenselects the current motion vector from the list.

As described above, in this embodiment, in the case where the referencepicture of the current block is a short-term reference picture and thereference picture of the co-located block is a long-term referencepicture, the current motion vector is not derived from the motion vectorof the co-located block.

It is extremely difficult to derive the current motion vector of highprediction accuracy, in the case where one of the current referencepicture and the co-located reference picture is a long-term referencepicture and the other one of the current reference picture and theco-located reference picture is a short-term reference picture. In viewof this, the image coding apparatus 500 and the image decoding apparatus600 according to this embodiment prevent prediction accuracy degradationby the operation described above.

Embodiment 3

An image coding apparatus and an image decoding apparatus according toEmbodiment 3 have the same structures as those in Embodiment 1. Hence,the operations of the image coding apparatus and the image decodingapparatus according to this embodiment are described below, using thestructure of the image coding apparatus 500 shown in FIG. 5 and thestructure of the image decoding apparatus 600 shown in FIG. 6 .

The image coding apparatus 500 according to this embodiment performs theoperation shown in FIG. 7 , as in Embodiment 1. The image decodingapparatus 600 according to this embodiment performs the operation shownin FIG. 8 , as in Embodiment 1. This embodiment differs from Embodiment1 in the current motion vector derivation process. This is described indetail below.

FIG. 12 is a flowchart showing details of the derivation processaccording to this embodiment. The inter predicting unit 511 according tothis embodiment performs the operation shown in FIG. 12 , instead of theoperation shown in FIG. 9 . The following mainly describes the operationof the inter predicting unit 511 shown in FIG. 5 . The operation of theinter predicting unit 608 shown in FIG. 6 is the same as the operationof the inter predicting unit 511 shown in FIG. 5 , with “coding” beingreplaced with “decoding”.

First, the inter predicting unit 511 selects the co-located picture fromthe plurality of available reference pictures (Step S1201). Next, theinter predicting unit 511 selects the co-located block in the co-locatedpicture (Step S1202). The inter predicting unit 511 then identifies theco-located reference picture and the co-located motion vector (StepS1203).

Following this, the inter predicting unit 511 determines whether or notthe current reference picture is a long-term reference picture (StepS1204). In the case of determining that the current reference picture isa long-term reference picture (Step S1204: Yes), the inter predictingunit 511 derives the current motion vector by the first derivationscheme same as in Embodiment 1 (Step S1205).

In the case of determining that the current reference picture is not along-term reference picture (Step S1204: No), the inter predicting unit511 determines whether or not the co-located reference picture is along-term reference picture (Step S1206).

In the case of determining that the co-located reference picture is nota long-term reference picture (Step S1206: No), the inter predictingunit 511 derives the current motion vector by the second derivationscheme same as in Embodiment 1 (Step S1207). That is, in the case ofdetermining that the current reference picture and the co-locatedreference picture are each a short-term reference picture, the interpredicting unit 511 derives the current motion vector by the secondderivation scheme.

In the case of determining that the co-located reference picture is along-term reference picture (Step S1206: Yes), the inter predicting unit511 selects another co-located picture (Step S1208). The interpredicting unit 511 then selects another co-located block in the otherco-located picture (Step S1209). In the example shown in FIG. 12 , ablock coded with reference to a short-term reference picture is selectedas the other co-located block.

After this, the inter predicting unit 511 identifies the co-locatedreference picture and the co-located motion vector corresponding to theother co-located block (Step S1210). The inter predicting unit 511 thenderives the current motion vector by the second derivation scheme thatuses POC-based scaling (Step S1211).

In detail, in the case where the reference picture of the current blockis a short-term reference picture and the reference picture of theco-located block is a long-term reference picture, the inter predictingunit 511 does not derive the current motion vector from the motionvector of the co-located block.

The inter predicting unit 511 instead selects another co-locatedpicture. The inter predicting unit 511 further selects anotherco-located block coded with reference to a short-term reference picture,from the selected other co-located picture. The inter predicting unit511 derives the current motion vector from the motion vector of theselected other co-located block.

As an example, in the case where the current reference picture is ashort-term reference picture and the co-located reference picture is along-term reference picture, the inter predicting unit 511 searches fora picture that includes a block coded with reference to a short-termreference picture. The inter predicting unit 511 selects the picturethat includes the block coded with reference to the short-term referencepicture, as the other co-located picture.

As another example, in the case where the current reference picture is ashort-term reference picture and the co-located reference picture is along-term reference picture, the inter predicting unit 511 firstsearches for a picture that includes a block coded with reference to ashort-term reference picture.

In the case where the picture that includes the block coded withreference to the short-term reference picture is present, the interpredicting unit 511 selects the picture as the other co-located picture.

In the case where the picture that includes the block coded withreference to the short-term reference picture is not present, the interpredicting unit 511 searches for a picture that includes a block codedwith reference to a long-term reference picture. The inter predictingunit 511 selects the picture that includes the block coded withreference to the long-term reference picture, as the other co-locatedpicture.

For example, in the case where the picture RefPicList0[0] is theco-located picture, the picture RefPicList1[0] is the other co-locatedpicture. In the case where the picture RefPicList1[0] is the co-locatedpicture, the picture RefPicList0[0] is the other co-located picture.

In other words, the picture listed first in one of the two referencepicture lists used for coding of B pictures (bi-predictive coding) isthe co-located picture, and the picture listed first in the other one ofthe two reference picture lists is the other co-located picture.

The following describes a more specific example of the process ofderiving the current motion vector with reference to FIG. 12 again. Thederivation process described earlier may be changed as follows.

First, the inter predicting unit 511 selects one of the pictureRefPicList0[0] and the picture RefPicList1[0], as the co-located picture(Step S1201). The inter predicting unit 511 selects, from the selectedco-located picture, the first block including the sample c0 shown inFIG. 11 as the co-located block, and identifies the co-located referencepicture (Steps S1202 and S1203).

Following this, the inter predicting unit 511 determines whether or notthe co-located block is available. In the case where the currentreference picture is a short-term reference picture and the co-locatedreference picture is a long-term reference picture, the inter predictingunit 511 determines that the co-located block is not available (StepsS1204 and S1206).

In the case where the co-located block is not available, the interpredicting unit 511 newly selects an available co-located block. Forexample, the inter predicting unit 511 selects the second blockincluding the sample c1 shown in FIG. 11 , as the co-located block. Theinter predicting unit 511 then identifies the co-located referencepicture.

In the case where the available co-located block is not selected, theinter predicting unit 511 selects another co-located picture. Here, theinter predicting unit 511 selects the other one of the pictureRefPicList0[0] and the picture RefPicList1[0], as the co-located picture(Step S1208).

The inter predicting unit 511 selects, from the selected co-locatedpicture, the first block including the sample c0 shown in FIG. 1 as theco-located block, and identifies the co-located reference picture (StepsS1209 and S1210).

Following this, the inter predicting unit 511 determines whether or notthe co-located block is available. As in the previous determination, inthe case where the current reference picture is a short-term referencepicture and the co-located reference picture is a long-term referencepicture, the inter predicting unit 511 determines that the co-locatedblock is not available.

In the case where the co-located block is not available, the interpredicting unit 511 newly selects an available co-located block (StepS1209). In detail, the inter predicting unit 511 selects the secondblock including the sample c1 shown in FIG. 11 , as the co-locatedblock. The inter predicting unit 511 then identifies the co-locatedreference picture (Step S1210).

In the case where the available co-located block is eventually selected,the inter predicting unit 511 sets the temporal motion vector predictoras available. In the case where the available co-located block iseventually not selected, the inter predicting unit 511 sets the temporalmotion vector predictor as not available.

In the case where the temporal motion vector predictor is set asavailable, the inter predicting unit 511 identifies the motion vector ofthe co-located block as the base motion vector (Steps S1203 and S1210).In the case where the co-located block has a plurality of motionvectors, that is, in the case where the co-located block is coded usinga plurality of motion vectors, the inter predicting unit 511 selects thebase motion vector according to predetermined priority order as inEmbodiment 1.

In the case where any of the current reference picture and theco-located reference picture is a long-term reference picture (StepS1204: Yes), the inter predicting unit 511 derives the base motionvector as the temporal motion vector predictor (Step S1205).

In the case where none of the current reference picture and theco-located reference picture is a long-term reference picture (StepS1204: No), on the other hand, the inter predicting unit 511 derives thetemporal motion vector predictor from the base motion vector byPOC-based scaling (Steps S1207 and S1211).

In the case where the temporal motion vector predictor is set as notavailable, the inter predicting unit 511 does not derive the temporalmotion vector predictor.

As in Embodiment 1, the inter predicting unit 511 adds the temporalmotion vector predictor set as available, to the list as the candidatefor the current motion vector. The inter predicting unit 511 thenselects the current motion vector from the list.

As described above, the image coding apparatus 500 and the imagedecoding apparatus 600 according to this embodiment select the blocksuitable for current motion vector derivation from a plurality ofpictures, and derive the current motion vector from the motion vector ofthe selected block. This contributes to improved coding efficiency.

Embodiment 4

Embodiment 4 confirmatorily describes the characteristic structures andthe characteristic procedures included in Embodiments 1 to 3.

FIG. 13A is a block diagram of an image coding apparatus according tothis embodiment. An image coding apparatus 1300 shown in FIG. 13A codeseach of blocks of pictures. The image coding apparatus 1300 includes aderiving unit 1301, an adding unit 1302, a selecting unit 1303, and acoder 1304.

For example, the deriving unit 1301, the adding unit 1302, and theselecting unit 1303 correspond to the inter predicting unit 511 shown inFIG. 5 and the like, and the coder 1304 corresponds to the entropy coder504 shown in FIG. 5 and the like.

FIG. 13B is a flowchart showing an operation of the image codingapparatus 1300 shown in FIG. 13A.

The deriving unit 1301 derives a candidate for a motion vector of acurrent block, from a motion vector of a co-located block (Step S1301).The co-located block is a block included in a picture different from apicture that includes the current block to be coded.

In the derivation of the candidate, the deriving unit 1301 determineswhether a reference picture of the current block is a long-termreference picture or a short-term reference picture. The deriving unit1301 also determines whether a reference picture of the co-located blockis a long-term reference picture or a short-term reference picture.

In the case of determining that the reference picture of the currentblock and the reference picture of the co-located block are each along-term reference picture, the deriving unit 1301 derives thecandidate from the motion vector of the co-located block by a firstderivation scheme. The first derivation scheme is a derivation schemethat does not involve scaling based on a temporal distance.

In the case of determining that the reference picture of the currentblock and the reference picture of the co-located block are each ashort-term reference picture, on the other hand, the deriving unit 1301derives the candidate from the motion vector of the co-located block bya second derivation scheme. The second derivation scheme is a derivationscheme that involves scaling based on a temporal distance.

The adding unit 1302 adds the derived candidate to a list (Step S1302).The selecting unit 1303 selects the motion vector of the current blockfrom the list to which the candidate is added (Step S1303).

The coder 1304 codes the current block using the selected motion vectorand the reference picture of the current block (Step S1304).

FIG. 14A is a block diagram of an image decoding apparatus according tothis embodiment. An image decoding apparatus 1400 shown in FIG. 14Adecodes each of blocks of pictures. The image decoding apparatus 1400includes a deriving unit 1401, an adding unit 1402, a selecting unit1403, and a decoder 1404.

For example, the deriving unit 1401, the adding unit 1402, and theselecting unit 1403 correspond to the inter predicting unit 608 shown inFIG. 6 and the like, and the decoder 1404 corresponds to the entropydecoder 601 shown in FIG. 6 and the like.

FIG. 14B is a flowchart showing an operation of the image decodingapparatus 1400 shown in FIG. 14A.

The deriving unit 1401 derives a candidate for a motion vector of acurrent block, from a motion vector of a co-located block (Step S1401).The co-located block is a block included in a picture different from apicture that includes a current block to be decoded.

In the derivation of the candidate, the deriving unit 1401 determineswhether a reference picture of the current block is a long-termreference picture or a short-term reference picture. The deriving unit1401 also determines whether a reference picture of the co-located blockis a long-term reference picture or a short-term reference picture.

In the case of determining that the reference picture of the currentblock and the reference picture of the co-located block are each along-term reference picture, the deriving unit 1401 derives thecandidate from the motion vector of the co-located block by a firstderivation scheme. The first derivation scheme is a derivation schemethat does not involve scaling based on a temporal distance.

In the case of determining that the reference picture of the currentblock and the reference picture of the co-located block are each ashort-term reference picture, on the other hand, the deriving unit 1401derives the candidate from the motion vector of the co-located block bya second derivation scheme. The second derivation scheme is a derivationscheme that involves scaling based on a temporal distance.

The adding unit 1402 adds the derived candidate to a list (Step S1402).The selecting unit 1403 selects the motion vector of the current blockfrom the list to which the candidate is added (Step S1403).

The decoder 1404 decodes the current block using the selected motionvector and the reference picture of the current block (Step S1404).

Through the process described above, the candidate for the currentmotion vector is appropriately derived from the motion vector of theco-located block, without being extremely large or small. Thiscontributes to improved prediction accuracy and improved codingefficiency.

Here, the deriving units 1301 and 1401 may each not derive the candidatefrom the motion vector of the co-located block, in the case ofdetermining that one of the reference picture of the current block andthe reference picture of the co-located block is a long-term referencepicture and the other one of the reference picture of the current blockand the reference picture of the co-located block is a short-termreference picture.

In this case, the deriving units 1301 and 1401 may each further selectanother co-located block coded or decoded with reference to a short-termreference picture, and derive the candidate from the other co-locatedblock by the second derivation scheme. As an alternative, the derivingunits 1301 and 1401 may each derive the candidate by another derivationscheme. As another alternative, the deriving units 1301 and 1401 mayeach eventually not derive the candidate corresponding to the temporalmotion vector predictor.

The deriving units 1301 and 1401 may determine whether the referencepicture of the current block is a long-term reference picture or ashort-term reference picture, using a temporal distance between thereference picture of the current block and the picture that includes thecurrent block.

The deriving units 1301 and 1401 may each determine whether thereference picture of the co-located block is a long-term referencepicture or a short-term reference picture, using a temporal distancebetween the reference picture of the co-located block and the picturethat includes the co-located block.

The deriving units 1301 and 1401 may each determine whether thereference picture of the co-located block is a long-term referencepicture or a short-term reference picture, in a period during which theco-located block is coded or decoded.

The deriving units 1301 and 1401 may each determine whether thereference picture of the co-located block is a long-term referencepicture or a short-term reference picture, in a period during which thecurrent block is coded or decoded.

The first derivation scheme may be a scheme of deriving the motionvector of the co-located block as the candidate. The second derivationscheme may be a scheme of deriving the candidate by scaling the motionvector of the co-located block using a ratio of the temporal distancebetween the reference picture of the current block and the picture thatincludes the current block to the temporal distance between thereference picture of the co-located block and the picture that includesthe co-located block.

The coder 1304 may further code information indicating whether thereference picture of the current block is a long-term reference pictureor a short-term reference picture, and information indicating whetherthe reference picture of the co-located block is a long-term referencepicture or a short-term reference picture.

The decoder 1404 may further decode information indicating whether thereference picture of the current block is a long-term reference pictureor a short-term reference picture, and information indicating whetherthe reference picture of the co-located block is a long-term referencepicture or a short-term reference picture.

The deriving unit 1401 may then determine whether the reference pictureof the current block is a long-term reference picture or a short-termreference picture using the decoded information, and determine whetherthe reference picture of the co-located block is a long-term referencepicture or a short-term reference picture using the decoded information.

Information indicating classification of each reference picture may bestored, as a parameter, in a bitstream at a location described below.

FIG. 15A is a diagram showing a first example of the storage location ofthe parameter indicating the reference picture classification. As shownin FIG. 15A, the parameter indicating the reference pictureclassification may be stored in a sequence header. The sequence headeris also referred to as a sequence parameter set.

FIG. 15B is a diagram showing a second example of the storage locationof the parameter indicating the reference picture classification. Asshown in FIG. 15B, the parameter indicating the reference pictureclassification may be stored in a picture header. The picture header isalso referred to as a picture parameter set.

FIG. 15C is a diagram showing a third example of the storage location ofthe parameter indicating the reference picture classification. As shownin FIG. 15C, the parameter indicating the reference pictureclassification may be stored in a slice header.

Information indicating a prediction mode (inter prediction or intraprediction) may be stored, as a parameter, in the bitstream at alocation described below.

FIG. 16 is a diagram showing an example of the storage location of theparameter indicating the prediction mode. As shown in FIG. 16 , theparameter may be stored in a CU header (coding unit header). Theparameter indicates whether a prediction unit in a coding unit is codedby inter prediction or intra prediction. This parameter may be used todetermine whether or not the co-located block is available.

Each of the structural elements in each of the above-describedembodiments may be configured in the form of an exclusive hardwareproduct, or may be realized by executing a software program suitable forthe structural element. Each of the structural elements may be realizedby means of a program executing unit, such as a CPU and a processor,reading and executing the software program recorded on a recordingmedium such as a hard disk or a semiconductor memory. Here, the softwareprogram for realizing the image coding apparatus and the like accordingto each of the embodiments is a program described below.

The program causes a computer to execute an image coding method ofcoding each of blocks of pictures, the image coding method including:deriving a candidate for a motion vector of a current block to be coded,from a motion vector of a co-located block which is a block included ina picture different from a picture that includes the current block;adding the derived candidate to a list; selecting the motion vector ofthe current block from the list to which the candidate is added; andcoding the current block using the selected motion vector and areference picture of the current block, wherein the deriving includes:determining whether the reference picture of the current block is along-term reference picture or a short-term reference picture, andwhether a reference picture of the co-located block is a long-termreference picture or a short-term reference picture; deriving thecandidate from the motion vector of the co-located block by a firstderivation scheme that does not involve scaling based on a temporaldistance, in the case of determining that each of the reference pictureof the current block and the reference picture of the co-located blockis a long-term reference picture; and deriving the candidate from themotion vector of the co-located block by a second derivation scheme thatinvolves scaling based on a temporal distance, in the case ofdetermining that each of the reference picture of the current block andthe reference picture of the co-located block is a short-term referencepicture.

The program may cause the computer to execute an image decoding methodof decoding each of blocks of pictures, the image decoding methodincluding: deriving a candidate for a motion vector of a current blockto be decoded, from a motion vector of a co-located block which is ablock included in a picture different from a picture that includes thecurrent block; adding the derived candidate to a list; selecting themotion vector of the current block from the list to which the candidateis added; and decoding the current block using the selected motionvector and a reference picture of the current block, wherein thederiving includes: determining whether the reference picture of thecurrent block is a long-term reference picture or a short-term referencepicture, and whether a reference picture of the co-located block is along-term reference picture or a short-term reference picture; derivingthe candidate from the motion vector of the co-located block by a firstderivation scheme that does not involve scaling based on a temporaldistance, in the case of determining that each of the reference pictureof the current block and the reference picture of the co-located blockis a long-term reference picture; and deriving the candidate from themotion vector of the co-located block by a second derivation scheme thatinvolves scaling based on a temporal distance, in the case ofdetermining that each of the reference picture of the current block andthe reference picture of the co-located block is a short-term referencepicture.

Each of the structural elements may be a circuit. These circuits maywholly constitute one circuit, or be separate circuits. Each of thestructural elements may be realized by a general-purpose processor orrealized by a special-purpose processor.

The herein disclosed subject matter is to be considered descriptive andillustrative only, and the appended Claims are of a scope intended tocover and encompass not only the particular embodiments disclosed, butalso equivalent structures, methods, and/or uses.

For example, an image coding and decoding apparatus may include theimage coding apparatus and the image decoding apparatus. A processexecuted by a specific processing unit may be executed by anotherprocessing unit. Processes may be executed in different order, and twoor more processes may be executed in parallel.

Embodiment 5

The processing described in each of embodiments can be simplyimplemented in an independent computer system, by recording, in arecording medium, a program for implementing the configurations of themoving picture coding method (image coding method) and the movingpicture decoding method (image decoding method) described in each ofembodiments. The recording media may be any recording media as long asthe program can be recorded, such as a magnetic disk, an optical disk, amagnetic optical disk, an IC card, and a semiconductor memory.

Hereinafter, the applications to the moving picture coding method (imagecoding method) and the moving picture decoding method (image decodingmethod) described in each of embodiments and systems using thereof willbe described. The system has a feature of having an image coding anddecoding apparatus that includes an image coding apparatus using theimage coding method and an image decoding apparatus using the imagedecoding method. Other configurations in the system can be changed asappropriate depending on the cases.

FIG. 17 illustrates an overall configuration of a content providingsystem ex100 for implementing content distribution services. The areafor providing communication services is divided into cells of desiredsize, and base stations ex106, ex107, ex108, ex109, and ex110 which arefixed wireless stations are placed in each of the cells.

The content providing system ex100 is connected to devices, such as acomputer ex111, a personal digital assistant (PDA) ex112, a cameraex113, a cellular phone ex114 and a game machine ex115, via the Internetex101, an Internet service provider ex102, a telephone network ex104, aswell as the base stations ex106 to ex110, respectively.

However, the configuration of the content providing system ex100 is notlimited to the configuration shown in FIG. 17 , and a combination inwhich any of the elements are connected is acceptable. In addition, eachdevice may be directly connected to the telephone network ex104, ratherthan via the base stations ex106 to ex110 which are the fixed wirelessstations. Furthermore, the devices may be interconnected to each othervia a short distance wireless communication and others.

The camera ex113, such as a digital video camera, is capable ofcapturing video. A camera ex116, such as a digital camera, is capable ofcapturing both still images and video. Furthermore, the cellular phoneex114 may be the one that meets any of the standards such as GlobalSystem for Mobile Communications (GSM) (registered trademark), CodeDivision Multiple Access (CDMA), Wideband-Code Division Multiple Access(W-CDMA), Long Term Evolution (LTE), and High Speed Packet Access(HSPA). Alternatively, the cellular phone ex114 may be a PersonalHandyphone System (PHS).

In the content providing system ex100, a streaming server ex103 isconnected to the camera ex113 and others via the telephone network ex104and the base station ex109, which enables distribution of images of alive show and others. In such a distribution, a content (for example,video of a music live show) captured by the user using the camera ex113is coded as described above in each of embodiments (i.e., the camerafunctions as the image coding apparatus according to an aspect of thepresent disclosure), and the coded content is transmitted to thestreaming server ex103. On the other hand, the streaming server ex103carries out stream distribution of the transmitted content data to theclients upon their requests. The clients include the computer ex111, thePDA ex112, the camera ex113, the cellular phone ex114, and the gamemachine ex115 that are capable of decoding the above-mentioned codeddata. Each of the devices that have received the distributed datadecodes and reproduces the coded data (i.e., functions as the imagedecoding apparatus according to an aspect of the present disclosure).

The captured data may be coded by the camera ex113 or the streamingserver ex103 that transmits the data, or the coding processes may beshared between the camera ex113 and the streaming server ex103.Similarly, the distributed data may be decoded by the clients or thestreaming server ex103, or the decoding processes may be shared betweenthe clients and the streaming server ex103. Furthermore, the data of thestill images and video captured by not only the camera ex113 but alsothe camera ex116 may be transmitted to the streaming server ex103through the computer ex111. The coding processes may be performed by thecamera ex116, the computer ex111, or the streaming server ex103, orshared among them.

Furthermore, the coding and decoding processes may be performed by anLSI ex500 generally included in each of the computer ex111 and thedevices. The LSI ex500 may be configured of a single chip or a pluralityof chips. Software for coding and decoding video may be integrated intosome type of a recording medium (such as a CD-ROM, a flexible disk, anda hard disk) that is readable by the computer ex111 and others, and thecoding and decoding processes may be performed using the software.Furthermore, when the cellular phone ex114 is equipped with a camera,the video data obtained by the camera may be transmitted. The video datais data coded by the LSI ex500 included in the cellular phone ex114.

Furthermore, the streaming server ex103 may be composed of servers andcomputers, and may decentralize data and process the decentralized data,record, or distribute data.

As described above, the clients may receive and reproduce the coded datain the content providing system ex100. In other words, the clients canreceive and decode information transmitted by the user, and reproducethe decoded data in real time in the content providing system ex100, sothat the user who does not have any particular right and equipment canimplement personal broadcasting.

Aside from the example of the content providing system ex100, at leastone of the moving picture coding apparatus (image coding apparatus) andthe moving picture decoding apparatus (image decoding apparatus)described in each of embodiments may be implemented in a digitalbroadcasting system ex200 illustrated in FIG. 18 . More specifically, abroadcast station ex201 communicates or transmits, via radio waves to abroadcast satellite ex202, multiplexed data obtained by multiplexingaudio data and others onto video data. The video data is data coded bythe moving picture coding method described in each of embodiments (i.e.,data coded by the image coding apparatus according to an aspect of thepresent disclosure). Upon receipt of the multiplexed data, the broadcastsatellite ex202 transmits radio waves for broadcasting. Then, a home-useantenna ex204 with a satellite broadcast reception function receives theradio waves. Next, a device such as a television (receiver) ex300 and aset top box (STB) ex217 decodes the received multiplexed data, andreproduces the decoded data (i.e., functions as the image decodingapparatus according to an aspect of the present disclosure).

Furthermore, a reader/recorder ex218 (i) reads and decodes themultiplexed data recorded on a recording medium ex215, such as a DVD anda BD, or (i) codes video signals in the recording medium ex215, and insome cases, writes data obtained by multiplexing an audio signal on thecoded data. The reader/recorder ex218 can include the moving picturedecoding apparatus or the moving picture coding apparatus as shown ineach of embodiments. In this case, the reproduced video signals aredisplayed on the monitor ex219, and can be reproduced by another deviceor system using the recording medium ex215 on which the multiplexed datais recorded. It is also possible to implement the moving picturedecoding apparatus in the set top box ex217 connected to the cable ex203for a cable television or to the antenna ex204 for satellite and/orterrestrial broadcasting, so as to display the video signals on themonitor ex219 of the television ex300. The moving picture decodingapparatus may be implemented not in the set top box but in thetelevision ex300.

FIG. 19 illustrates the television (receiver) ex300 that uses the movingpicture coding method and the moving picture decoding method describedin each of embodiments. The television ex300 includes: a tuner ex301that obtains or provides multiplexed data obtained by multiplexing audiodata onto video data, through the antenna ex204 or the cable ex203, etc.that receives a broadcast; a modulation/demodulation unit ex302 thatdemodulates the received multiplexed data or modulates data intomultiplexed data to be supplied outside; and amultiplexing/demultiplexing unit ex303 that demultiplexes the modulatedmultiplexed data into video data and audio data, or multiplexes videodata and audio data coded by a signal processing unit ex306 into data.

The television ex300 further includes: a signal processing unit ex306including an audio signal processing unit ex304 and a video signalprocessing unit ex305 that decode audio data and video data and codeaudio data and video data, respectively (which function as the imagecoding apparatus and the image decoding apparatus according to theaspects of the present disclosure); and an output unit ex309 including aspeaker ex307 that provides the decoded audio signal, and a display unitex308 that displays the decoded video signal, such as a display.Furthermore, the television ex300 includes an interface unit ex317including an operation input unit ex312 that receives an input of a useroperation. Furthermore, the television ex300 includes a control unitex310 that controls overall each constituent element of the televisionex300, and a power supply circuit unit ex311 that supplies power to eachof the elements. Other than the operation input unit ex312, theinterface unit ex317 may include: a bridge ex313 that is connected to anexternal device, such as the reader/recorder ex218; a slot unit ex314for enabling attachment of the recording medium ex216, such as an SDcard; a driver ex315 to be connected to an external recording medium,such as a hard disk; and a modem ex316 to be connected to a telephonenetwork. Here, the recording medium ex216 can electrically recordinformation using a non-volatile/volatile semiconductor memory elementfor storage. The constituent elements of the television ex300 areconnected to each other through a synchronous bus.

First, the configuration in which the television ex300 decodesmultiplexed data obtained from outside through the antenna ex204 andothers and reproduces the decoded data will be described. In thetelevision ex300, upon a user operation through a remote controllerex220 and others, the multiplexing/demultiplexing unit ex303demultiplexes the multiplexed data demodulated by themodulation/demodulation unit ex302, under control of the control unitex310 including a CPU. Furthermore, the audio signal processing unitex304 decodes the demultiplexed audio data, and the video signalprocessing unit ex305 decodes the demultiplexed video data, using thedecoding method described in each of embodiments, in the televisionex300. The output unit ex309 provides the decoded video signal and audiosignal outside, respectively. When the output unit ex309 provides thevideo signal and the audio signal, the signals may be temporarily storedin buffers ex318 and ex319, and others so that the signals arereproduced in synchronization with each other. Furthermore, thetelevision ex300 may read multiplexed data not through a broadcast andothers but from the recording media ex215 and ex216, such as a magneticdisk, an optical disk, and a SD card. Next, a configuration in which thetelevision ex300 codes an audio signal and a video signal, and transmitsthe data outside or writes the data on a recording medium will bedescribed. In the television ex300, upon a user operation through theremote controller ex220 and others, the audio signal processing unitex304 codes an audio signal, and the video signal processing unit ex305codes a video signal, under control of the control unit ex310 using thecoding method described in each of embodiments. Themultiplexing/demultiplexing unit ex303 multiplexes the coded videosignal and audio signal, and provides the resulting signal outside. Whenthe multiplexing/demultiplexing unit ex303 multiplexes the video signaland the audio signal, the signals may be temporarily stored in thebuffers ex320 and ex321, and others so that the signals are reproducedin synchronization with each other. Here, the buffers ex318, ex319,ex320, and ex321 may be plural as illustrated, or at least one buffermay be shared in the television ex300. Furthermore, data may be storedin a buffer so that the system overflow and underflow may be avoidedbetween the modulation/demodulation unit ex302 and themultiplexing/demultiplexing unit ex303, for example.

Furthermore, the television ex300 may include a configuration forreceiving an AV input from a microphone or a camera other than theconfiguration for obtaining audio and video data from a broadcast or arecording medium, and may code the obtained data. Although thetelevision ex300 can code, multiplex, and provide outside data in thedescription, it may be capable of only receiving, decoding, andproviding outside data but not the coding, multiplexing, and providingoutside data.

Furthermore, when the reader/recorder ex218 reads or writes multiplexeddata from or on a recording medium, one of the television ex300 and thereader/recorder ex218 may decode or code the multiplexed data, and thetelevision ex300 and the reader/recorder ex218 may share the decoding orcoding.

As an example, FIG. 20 illustrates a configuration of an informationreproducing/recording unit ex400 when data is read or written from or onan optical disk. The information reproducing/recording unit ex400includes constituent elements ex401, ex402, ex403, ex404, ex405, ex406,and ex407 to be described hereinafter. The optical head ex401 irradiatesa laser spot in a recording surface of the recording medium ex215 thatis an optical disk to write information, and detects reflected lightfrom the recording surface of the recording medium ex215 to read theinformation. The modulation recording unit ex402 electrically drives asemiconductor laser included in the optical head ex401, and modulatesthe laser light according to recorded data. The reproductiondemodulating unit ex403 amplifies a reproduction signal obtained byelectrically detecting the reflected light from the recording surfaceusing a photo detector included in the optical head ex401, anddemodulates the reproduction signal by separating a signal componentrecorded on the recording medium ex215 to reproduce the necessaryinformation. The buffer ex404 temporarily holds the information to berecorded on the recording medium ex215 and the information reproducedfrom the recording medium ex215. The disk motor ex405 rotates therecording medium ex215. The servo control unit ex406 moves the opticalhead ex401 to a predetermined information track while controlling therotation drive of the disk motor ex405 so as to follow the laser spot.The system control unit ex407 controls overall the informationreproducing/recording unit ex400. The reading and writing processes canbe implemented by the system control unit ex407 using variousinformation stored in the buffer ex404 and generating and adding newinformation as necessary, and by the modulation recording unit ex402,the reproduction demodulating unit ex403, and the servo control unitex406 that record and reproduce information through the optical headex401 while being operated in a coordinated manner. The system controlunit ex407 includes, for example, a microprocessor, and executesprocessing by causing a computer to execute a program for read andwrite.

Although the optical head ex401 irradiates a laser spot in thedescription, it may perform high-density recording using near fieldlight.

FIG. 21 illustrates the recording medium ex215 that is the optical disk.On the recording surface of the recording medium ex215, guide groovesare spirally formed, and an information track ex230 records, in advance,address information indicating an absolute position on the diskaccording to change in a shape of the guide grooves. The addressinformation includes information for determining positions of recordingblocks ex231 that are a unit for recording data. Reproducing theinformation track ex230 and reading the address information in anapparatus that records and reproduces data can lead to determination ofthe positions of the recording blocks. Furthermore, the recording mediumex215 includes a data recording area ex233, an inner circumference areaex232, and an outer circumference area ex234. The data recording areaex233 is an area for use in recording the user data. The innercircumference area ex232 and the outer circumference area ex234 that areinside and outside of the data recording area ex233, respectively arefor specific use except for recording the user data. The informationreproducing/recording unit 400 reads and writes coded audio, coded videodata, or multiplexed data obtained by multiplexing the coded audio andvideo data, from and on the data recording area ex233 of the recordingmedium ex215.

Although an optical disk having a layer, such as a DVD and a BD isdescribed as an example in the description, the optical disk is notlimited to such, and may be an optical disk having a multilayerstructure and capable of being recorded on a part other than thesurface. Furthermore, the optical disk may have a structure formultidimensional recording/reproduction, such as recording ofinformation using light of colors with different wavelengths in the sameportion of the optical disk and for recording information havingdifferent layers from various angles.

Furthermore, a car ex210 having an antenna ex205 can receive data fromthe satellite ex202 and others, and reproduce video on a display devicesuch as a car navigation system ex211 set in the car ex210, in thedigital broadcasting system ex200. Here, a configuration of the carnavigation system ex211 will be a configuration, for example, includinga GPS receiving unit from the configuration illustrated in FIG. 19 . Thesame will be true for the configuration of the computer ex111, thecellular phone ex114, and others.

FIG. 22A illustrates the cellular phone ex114 that uses the movingpicture coding method and the moving picture decoding method describedin embodiments. The cellular phone ex114 includes: an antenna ex350 fortransmitting and receiving radio waves through the base station ex110; acamera unit ex365 capable of capturing moving and still images; and adisplay unit ex358 such as a liquid crystal display for displaying thedata such as decoded video captured by the camera unit ex365 or receivedby the antenna ex350. The cellular phone ex114 further includes: a mainbody unit including an operation key unit ex366; an audio output unitex357 such as a speaker for output of audio; an audio input unit ex356such as a microphone for input of audio; a memory unit ex367 for storingcaptured video or still pictures, recorded audio, coded or decoded dataof the received video, the still pictures, e-mails, or others; and aslot unit ex364 that is an interface unit for a recording medium thatstores data in the same manner as the memory unit ex367.

Next, an example of a configuration of the cellular phone ex114 will bedescribed with reference to FIG. 22B. In the cellular phone ex114, amain control unit ex360 designed to control overall each unit of themain body including the display unit ex358 as well as the operation keyunit ex366 is connected mutually, via a synchronous bus ex370, to apower supply circuit unit ex361, an operation input control unit ex362,a video signal processing unit ex355, a camera interface unit ex363, aliquid crystal display (LCD) control unit ex359, amodulation/demodulation unit ex352, a multiplexing/demultiplexing unitex353, an audio signal processing unit ex354, the slot unit ex364, andthe memory unit ex367.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex361 supplies the respective units withpower from a battery pack so as to activate the cell phone ex114.

In the cellular phone ex114, the audio signal processing unit ex354converts the audio signals collected by the audio input unit ex356 invoice conversation mode into digital audio signals under the control ofthe main control unit ex360 including a CPU, ROM, and RAM. Then, themodulation/demodulation unit ex352 performs spread spectrum processingon the digital audio signals, and the transmitting and receiving unitex351 performs digital-to-analog conversion and frequency conversion onthe data, so as to transmit the resulting data via the antenna ex350.Also, in the cellular phone ex114, the transmitting and receiving unitex351 amplifies the data received by the antenna ex350 in voiceconversation mode and performs frequency conversion and theanalog-to-digital conversion on the data. Then, themodulation/demodulation unit ex352 performs inverse spread spectrumprocessing on the data, and the audio signal processing unit ex354converts it into analog audio signals, so as to output them via theaudio output unit ex357.

Furthermore, when an e-mail in data communication mode is transmitted,text data of the e-mail inputted by operating the operation key unitex366 and others of the main body is sent out to the main control unitex360 via the operation input control unit ex362. The main control unitex360 causes the modulation/demodulation unit ex352 to perform spreadspectrum processing on the text data, and the transmitting and receivingunit ex351 performs the digital-to-analog conversion and the frequencyconversion on the resulting data to transmit the data to the basestation ex110 via the antenna ex350. When an e-mail is received,processing that is approximately inverse to the processing fortransmitting an e-mail is performed on the received data, and theresulting data is provided to the display unit ex358.

When video, still images, or video and audio in data communication modeis or are transmitted, the video signal processing unit ex355 compressesand codes video signals supplied from the camera unit ex365 using themoving picture coding method shown in each of embodiments (i.e.,functions as the image coding apparatus according to the aspect of thepresent disclosure), and transmits the coded video data to themultiplexing/demultiplexing unit ex353. In contrast, during when thecamera unit ex365 captures video, still images, and others, the audiosignal processing unit ex354 codes audio signals collected by the audioinput unit ex356, and transmits the coded audio data to themultiplexing/demultiplexing unit ex353.

The multiplexing/demultiplexing unit ex353 multiplexes the coded videodata supplied from the video signal processing unit ex355 and the codedaudio data supplied from the audio signal processing unit ex354, using apredetermined method. Then, the modulation/demodulation unit(modulation/demodulation circuit unit) ex352 performs spread spectrumprocessing on the multiplexed data, and the transmitting and receivingunit ex351 performs digital-to-analog conversion and frequencyconversion on the data so as to transmit the resulting data via theantenna ex350.

When receiving data of a video file which is linked to a Web page andothers in data communication mode or when receiving an e-mail with videoand/or audio attached, in order to decode the multiplexed data receivedvia the antenna ex350, the multiplexing/demultiplexing unit ex353demultiplexes the multiplexed data into a video data bit stream and anaudio data bit stream, and supplies the video signal processing unitex355 with the coded video data and the audio signal processing unitex354 with the coded audio data, through the synchronous bus ex370. Thevideo signal processing unit ex355 decodes the video signal using amoving picture decoding method corresponding to the moving picturecoding method shown in each of embodiments (i.e., functions as the imagedecoding apparatus according to the aspect of the present disclosure),and then the display unit ex358 displays, for instance, the video andstill images included in the video file linked to the Web page via theLCD control unit ex359. Furthermore, the audio signal processing unitex354 decodes the audio signal, and the audio output unit ex357 providesthe audio.

Furthermore, similarly to the television ex300, a terminal such as thecellular phone ex114 probably have 3 types of implementationconfigurations including not only (i) a transmitting and receivingterminal including both a coding apparatus and a decoding apparatus, butalso (ii) a transmitting terminal including only a coding apparatus and(iii) a receiving terminal including only a decoding apparatus. Althoughthe digital broadcasting system ex200 receives and transmits themultiplexed data obtained by multiplexing audio data onto video data inthe description, the multiplexed data may be data obtained bymultiplexing not audio data but character data related to video ontovideo data, and may be not multiplexed data but video data itself.

As such, the moving picture coding method and the moving picturedecoding method in each of embodiments can be used in any of the devicesand systems described. Thus, the advantages described in each ofembodiments can be obtained.

Furthermore, various modifications and revisions can be made in any ofthe embodiments in the present disclosure.

Embodiment 6

Video data can be generated by switching, as necessary, between (i) themoving picture coding method or the moving picture coding apparatusshown in each of embodiments and (ii) a moving picture coding method ora moving picture coding apparatus in conformity with a differentstandard, such as MPEG-2, MPEG-4 AVC, and VC-1.

Here, when a plurality of video data that conforms to the differentstandards is generated and is then decoded, the decoding methods need tobe selected to conform to the different standards. However, since towhich standard each of the plurality of the video data to be decodedconform cannot be detected, there is a problem that an appropriatedecoding method cannot be selected.

In order to solve the problem, multiplexed data obtained by multiplexingaudio data and others onto video data has a structure includingidentification information indicating to which standard the video dataconforms. The specific structure of the multiplexed data including thevideo data generated in the moving picture coding method and by themoving picture coding apparatus shown in each of embodiments will behereinafter described. The multiplexed data is a digital stream in theMPEG-2 Transport Stream format.

FIG. 23 illustrates a structure of the multiplexed data. As illustratedin FIG. 23 , the multiplexed data can be obtained by multiplexing atleast one of a video stream, an audio stream, a presentation graphicsstream (PG), and an interactive graphics stream. The video streamrepresents primary video and secondary video of a movie, the audiostream (IG) represents a primary audio part and a secondary audio partto be mixed with the primary audio part, and the presentation graphicsstream represents subtitles of the movie. Here, the primary video isnormal video to be displayed on a screen, and the secondary video isvideo to be displayed on a smaller window in the primary video.Furthermore, the interactive graphics stream represents an interactivescreen to be generated by arranging the GUI components on a screen. Thevideo stream is coded in the moving picture coding method or by themoving picture coding apparatus shown in each of embodiments, or in amoving picture coding method or by a moving picture coding apparatus inconformity with a conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1. The audio stream is coded in accordance with a standard, such asDolby-AC-3, Dolby Digital Plus, MLP, DTS, DTS-HD, and linear PCM.

Each stream included in the multiplexed data is identified by PID. Forexample, 0x1011 is allocated to the video stream to be used for video ofa movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to0x121F are allocated to the presentation graphics streams, 0x1400 to0x141F are allocated to the interactive graphics streams, 0x1B00 to0x1B1F are allocated to the video streams to be used for secondary videoof the movie, and 0x1A00 to 0x1A1F are allocated to the audio streams tobe used for the secondary audio to be mixed with the primary audio.

FIG. 24 schematically illustrates how data is multiplexed. First, avideo stream ex235 composed of video frames and an audio stream ex238composed of audio frames are transformed into a stream of PES packetsex236 and a stream of PES packets ex239, and further into TS packetsex237 and TS packets ex240, respectively. Similarly, data of apresentation graphics stream ex241 and data of an interactive graphicsstream ex244 are transformed into a stream of PES packets ex242 and astream of PES packets ex245, and further into TS packets ex243 and TSpackets ex246, respectively. These TS packets are multiplexed into astream to obtain multiplexed data ex247.

FIG. 25 illustrates how a video stream is stored in a stream of PESpackets in more detail. The first bar in FIG. 25 shows a video framestream in a video stream. The second bar shows the stream of PESpackets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4 inFIG. 25 , the video stream is divided into pictures as I pictures, Bpictures, and P pictures each of which is a video presentation unit, andthe pictures are stored in a payload of each of the PES packets. Each ofthe PES packets has a PES header, and the PES header stores aPresentation Time-Stamp (PTS) indicating a display time of the picture,and a Decoding Time-Stamp (DTS) indicating a decoding time of thepicture.

FIG. 26 illustrates a format of TS packets to be finally written on themultiplexed data. Each of the TS packets is a 188-byte fixed lengthpacket including a 4-byte TS header having information, such as a PIDfor identifying a stream and a 184-byte TS payload for storing data. ThePES packets are divided, and stored in the TS payloads, respectively.When a BD ROM is used, each of the TS packets is given a 4-byteTP_Extra_Header, thus resulting in 192-byte source packets. The sourcepackets are written on the multiplexed data. The TP_Extra_Header storesinformation such as an Arrival_Time_Stamp (ATS). The ATS shows atransfer start time at which each of the TS packets is to be transferredto a PID filter. The source packets are arranged in the multiplexed dataas shown at the bottom of FIG. 26 . The numbers incrementing from thehead of the multiplexed data are called source packet numbers (SPNs).

Each of the TS packets included in the multiplexed data includes notonly streams of audio, video, subtitles and others, but also a ProgramAssociation Table (PAT), a Program Map Table (PMT), and a Program ClockReference (PCR). The PAT shows what a PID in a PMT used in themultiplexed data indicates, and a PID of the PAT itself is registered aszero. The PMT stores PIDs of the streams of video, audio, subtitles andothers included in the multiplexed data, and attribute information ofthe streams corresponding to the PIDs. The PMT also has variousdescriptors relating to the multiplexed data. The descriptors haveinformation such as copy control information showing whether copying ofthe multiplexed data is permitted or not. The PCR stores STC timeinformation corresponding to an ATS showing when the PCR packet istransferred to a decoder, in order to achieve synchronization between anArrival Time Clock (ATC) that is a time axis of ATSs, and an System TimeClock (STC) that is a time axis of PTSs and DTSs.

FIG. 27 illustrates the data structure of the PMT in detail. A PMTheader is disposed at the top of the PMT. The PMT header describes thelength of data included in the PMT and others. A plurality ofdescriptors relating to the multiplexed data is disposed after the PMTheader. Information such as the copy control information is described inthe descriptors. After the descriptors, a plurality of pieces of streaminformation relating to the streams included in the multiplexed data isdisposed. Each piece of stream information includes stream descriptorseach describing information, such as a stream type for identifying acompression codec of a stream, a stream PID, and stream attributeinformation (such as a frame rate or an aspect ratio). The streamdescriptors are equal in number to the number of streams in themultiplexed data.

When the multiplexed data is recorded on a recording medium and others,it is recorded together with multiplexed data information files.

Each of the multiplexed data information files is management informationof the multiplexed data as shown in FIG. 28 . The multiplexed datainformation files are in one to one correspondence with the multiplexeddata, and each of the files includes multiplexed data information,stream attribute information, and an entry map.

As illustrated in FIG. 28 , the multiplexed data information includes asystem rate, a reproduction start time, and a reproduction end time. Thesystem rate indicates the maximum transfer rate at which a system targetdecoder to be described later transfers the multiplexed data to a PIDfilter. The intervals of the ATSs included in the multiplexed data areset to not higher than a system rate. The reproduction start timeindicates a PTS in a video frame at the head of the multiplexed data. Aninterval of one frame is added to a PTS in a video frame at the end ofthe multiplexed data, and the PTS is set to the reproduction end time.

As shown in FIG. 29 , a piece of attribute information is registered inthe stream attribute information, for each PID of each stream includedin the multiplexed data. Each piece of attribute information hasdifferent information depending on whether the corresponding stream is avideo stream, an audio stream, a presentation graphics stream, or aninteractive graphics stream. Each piece of video stream attributeinformation carries information including what kind of compression codecis used for compressing the video stream, and the resolution, aspectratio and frame rate of the pieces of picture data that is included inthe video stream. Each piece of audio stream attribute informationcarries information including what kind of compression codec is used forcompressing the audio stream, how many channels are included in theaudio stream, which language the audio stream supports, and how high thesampling frequency is. The video stream attribute information and theaudio stream attribute information are used for initialization of adecoder before the player plays back the information.

In the present embodiment, the multiplexed data to be used is of astream type included in the PMT. Furthermore, when the multiplexed datais recorded on a recording medium, the video stream attributeinformation included in the multiplexed data information is used. Morespecifically, the moving picture coding method or the moving picturecoding apparatus described in each of embodiments includes a step or aunit for allocating unique information indicating video data generatedby the moving picture coding method or the moving picture codingapparatus in each of embodiments, to the stream type included in the PMTor the video stream attribute information. With the configuration, thevideo data generated by the moving picture coding method or the movingpicture coding apparatus described in each of embodiments can bedistinguished from video data that conforms to another standard.

Furthermore, FIG. 30 illustrates steps of the moving picture decodingmethod according to the present embodiment. In Step exS100, the streamtype included in the PMT or the video stream attribute informationincluded in the multiplexed data information is obtained from themultiplexed data. Next, in Step exS101, it is determined whether or notthe stream type or the video stream attribute information indicates thatthe multiplexed data is generated by the moving picture coding method orthe moving picture coding apparatus in each of embodiments. When it isdetermined that the stream type or the video stream attributeinformation indicates that the multiplexed data is generated by themoving picture coding method or the moving picture coding apparatus ineach of embodiments, in Step exS102, decoding is performed by the movingpicture decoding method in each of embodiments. Furthermore, when thestream type or the video stream attribute information indicatesconformance to the conventional standards, such as MPEG-2, MPEG-4 AVC,and VC-1, in Step exS103, decoding is performed by a moving picturedecoding method in conformity with the conventional standards.

As such, allocating a new unique value to the stream type or the videostream attribute information enables determination whether or not themoving picture decoding method or the moving picture decoding apparatusthat is described in each of embodiments can perform decoding. Even whenmultiplexed data that conforms to a different standard is input, anappropriate decoding method or apparatus can be selected. Thus, itbecomes possible to decode information without any error. Furthermore,the moving picture coding method or apparatus, or the moving picturedecoding method or apparatus in the present embodiment can be used inthe devices and systems described above.

Embodiment 7

Each of the moving picture coding method, the moving picture codingapparatus, the moving picture decoding method, and the moving picturedecoding apparatus in each of embodiments is typically achieved in theform of an integrated circuit or a Large Scale Integrated (LSI) circuit.As an example of the LSI, FIG. 31 illustrates a configuration of the LSIex500 that is made into one chip. The LSI ex500 includes elements ex501,ex502, ex503, ex504, ex505, ex506, ex507, ex508, and ex509 to bedescribed below, and the elements are connected to each other through abus ex510. The power supply circuit unit ex505 is activated by supplyingeach of the elements with power when the power supply circuit unit ex505is turned on.

For example, when coding is performed, the LSI ex500 receives an AVsignal from a microphone ex117, a camera ex113, and others through an AVIO ex509 under control of a control unit ex501 including a CPU ex502, amemory controller ex503, a stream controller ex504, and a drivingfrequency control unit ex512. The received AV signal is temporarilystored in an external memory ex511, such as an SDRAM. Under control ofthe control unit ex501, the stored data is segmented into data portionsaccording to the processing amount and speed to be transmitted to asignal processing unit ex507. Then, the signal processing unit ex507codes an audio signal and/or a video signal. Here, the coding of thevideo signal is the coding described in each of embodiments.Furthermore, the signal processing unit ex507 sometimes multiplexes thecoded audio data and the coded video data, and a stream IO ex506provides the multiplexed data outside. The provided multiplexed data istransmitted to the base station ex107, or written on the recordingmedium ex215. When data sets are multiplexed, the data should betemporarily stored in the buffer ex508 so that the data sets aresynchronized with each other.

Although the memory ex511 is an element outside the LSI ex500, it may beincluded in the LSI ex500. The buffer ex508 is not limited to onebuffer, but may be composed of buffers. Furthermore, the LSI ex500 maybe made into one chip or a plurality of chips.

Furthermore, although the control unit ex501 includes the CPU ex502, thememory controller ex503, the stream controller ex504, the drivingfrequency control unit ex512, the configuration of the control unitex501 is not limited to such. For example, the signal processing unitex507 may further include a CPU. Inclusion of another CPU in the signalprocessing unit ex507 can improve the processing speed. Furthermore, asanother example, the CPU ex502 may serve as or be a part of the signalprocessing unit ex507, and, for example, may include an audio signalprocessing unit. In such a case, the control unit ex501 includes thesignal processing unit ex507 or the CPU ex502 including a part of thesignal processing unit ex507.

The name used here is LSI, but it may also be called IC, system LSI,super LSI, or ultra LSI depending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI, and aspecial circuit or a general purpose processor and so forth can alsoachieve the integration. Field Programmable Gate Array (FPGA) that canbe programmed after manufacturing LSIs or a reconfigurable processorthat allows re-configuration of the connection or configuration of anLSI can be used for the same purpose.

In the future, with advancement in semiconductor technology, a brand-newtechnology may replace LSI. The functional blocks can be integratedusing such a technology. The possibility is that the present disclosureis applied to biotechnology.

Embodiment 8

When video data generated in the moving picture coding method or by themoving picture coding apparatus described in each of embodiments isdecoded, compared to when video data that conforms to a conventionalstandard, such as MPEG-2, MPEG-4 AVC, and VC-1 is decoded, theprocessing amount probably increases. Thus, the LSI ex500 needs to beset to a driving frequency higher than that of the CPU ex502 to be usedwhen video data in conformity with the conventional standard is decoded.However, when the driving frequency is set higher, there is a problemthat the power consumption increases.

In order to solve the problem, the moving picture decoding apparatus,such as the television ex300 and the LSI ex500 is configured todetermine to which standard the video data conforms, and switch betweenthe driving frequencies according to the determined standard. FIG. 32illustrates a configuration ex800 in the present embodiment. A drivingfrequency switching unit ex803 sets a driving frequency to a higherdriving frequency when video data is generated by the moving picturecoding method or the moving picture coding apparatus described in eachof embodiments. Then, the driving frequency switching unit ex803instructs a decoding processing unit ex801 that executes the movingpicture decoding method described in each of embodiments to decode thevideo data. When the video data conforms to the conventional standard,the driving frequency switching unit ex803 sets a driving frequency to alower driving frequency than that of the video data generated by themoving picture coding method or the moving picture coding apparatusdescribed in each of embodiments. Then, the driving frequency switchingunit ex803 instructs the decoding processing unit ex802 that conforms tothe conventional standard to decode the video data.

More specifically, the driving frequency switching unit ex803 includesthe CPU ex502 and the driving frequency control unit ex512 in FIG. 31 .Here, each of the decoding processing unit ex801 that executes themoving picture decoding method described in each of embodiments and thedecoding processing unit ex802 that conforms to the conventionalstandard corresponds to the signal processing unit ex507 in FIG. 31 .The CPU ex502 determines to which standard the video data conforms.Then, the driving frequency control unit ex512 determines a drivingfrequency based on a signal from the CPU ex502. Furthermore, the signalprocessing unit ex507 decodes the video data based on the signal fromthe CPU ex502. For example, the identification information described inEmbodiment 6 is probably used for identifying the video data. Theidentification information is not limited to the one described inEmbodiment 6 but may be any information as long as the informationindicates to which standard the video data conforms. For example, whenwhich standard video data conforms to can be determined based on anexternal signal for determining that the video data is used for atelevision or a disk, etc., the determination may be made based on suchan external signal. Furthermore, the CPU ex502 selects a drivingfrequency based on, for example, a look-up table in which the standardsof the video data are associated with the driving frequencies as shownin FIG. 34 . The driving frequency can be selected by storing thelook-up table in the buffer ex508 and in an internal memory of an LSI,and with reference to the look-up table by the CPU ex502.

FIG. 33 illustrates steps for executing a method in the presentembodiment. First, in Step exS200, the signal processing unit ex507obtains identification information from the multiplexed data. Next, inStep exS201, the CPU ex502 determines whether or not the video data isgenerated by the coding method and the coding apparatus described ineach of embodiments, based on the identification information. When thevideo data is generated by the moving picture coding method and themoving picture coding apparatus described in each of embodiments, inStep exS202, the CPU ex502 transmits a signal for setting the drivingfrequency to a higher driving frequency to the driving frequency controlunit ex512. Then, the driving frequency control unit ex512 sets thedriving frequency to the higher driving frequency. On the other hand,when the identification information indicates that the video dataconforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1, in Step exS203, the CPU ex502 transmits a signal for setting thedriving frequency to a lower driving frequency to the driving frequencycontrol unit ex512. Then, the driving frequency control unit ex512 setsthe driving frequency to the lower driving frequency than that in thecase where the video data is generated by the moving picture codingmethod and the moving picture coding apparatus described in each ofembodiment.

Furthermore, along with the switching of the driving frequencies, thepower conservation effect can be improved by changing the voltage to beapplied to the LSI ex500 or an apparatus including the LSI ex500. Forexample, when the driving frequency is set lower, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set to a voltage lower than that in the case where the drivingfrequency is set higher.

Furthermore, when the processing amount for decoding is larger, thedriving frequency may be set higher, and when the processing amount fordecoding is smaller, the driving frequency may be set lower as themethod for setting the driving frequency. Thus, the setting method isnot limited to the ones described above. For example, when theprocessing amount for decoding video data in conformity with MPEG-4 AVCis larger than the processing amount for decoding video data generatedby the moving picture coding method and the moving picture codingapparatus described in each of embodiments, the driving frequency isprobably set in reverse order to the setting described above.

Furthermore, the method for setting the driving frequency is not limitedto the method for setting the driving frequency lower. For example, whenthe identification information indicates that the video data isgenerated by the moving picture coding method and the moving picturecoding apparatus described in each of embodiments, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set higher. When the identification information indicates thatthe video data conforms to the conventional standard, such as MPEG-2,MPEG-4 AVC, and VC-1, the voltage to be applied to the LSI ex500 or theapparatus including the LSI ex500 is probably set lower. As anotherexample, when the identification information indicates that the videodata is generated by the moving picture coding method and the movingpicture coding apparatus described in each of embodiments, the drivingof the CPU ex502 does not probably have to be suspended. When theidentification information indicates that the video data conforms to theconventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, the drivingof the CPU ex502 is probably suspended at a given time because the CPUex502 has extra processing capacity. Even when the identificationinformation indicates that the video data is generated by the movingpicture coding method and the moving picture coding apparatus describedin each of embodiments, in the case where the CPU ex502 has extraprocessing capacity, the driving of the CPU ex502 is probably suspendedat a given time. In such a case, the suspending time is probably setshorter than that in the case where when the identification informationindicates that the video data conforms to the conventional standard,such as MPEG-2, MPEG-4 AVC, and VC-1.

Accordingly, the power conservation effect can be improved by switchingbetween the driving frequencies in accordance with the standard to whichthe video data conforms. Furthermore, when the LSI ex500 or theapparatus including the LSI ex500 is driven using a battery, the batterylife can be extended with the power conservation effect.

Embodiment 9

There are cases where a plurality of video data that conforms todifferent standards, is provided to the devices and systems, such as atelevision and a cellular phone. In order to enable decoding theplurality of video data that conforms to the different standards, thesignal processing unit ex507 of the LSI ex500 needs to conform to thedifferent standards. However, the problems of increase in the scale ofthe circuit of the LSI ex500 and increase in the cost arise with theindividual use of the signal processing units ex507 that conform to therespective standards.

In order to solve the problem, what is conceived is a configuration inwhich the decoding processing unit for implementing the moving picturedecoding method described in each of embodiments and the decodingprocessing unit that conforms to the conventional standard, such asMPEG-2, MPEG-4 AVC, and VC-1 are partly shared. Ex900 in FIG. 35A showsan example of the configuration. For example, the moving picturedecoding method described in each of embodiments and the moving picturedecoding method that conforms to MPEG-4 AVC have, partly in common, thedetails of processing, such as entropy coding, inverse quantization,deblocking filtering, and motion compensated prediction. The details ofprocessing to be shared probably include use of a decoding processingunit ex902 that conforms to MPEG-4 AVC. In contrast, a dedicateddecoding processing unit ex901 is probably used for other processingunique to an aspect of the present disclosure. Since the aspect of thepresent disclosure is characterized by inter prediction in particular,for example, the dedicated decoding processing unit ex901 is used forinter prediction. Otherwise, the decoding processing unit is probablyshared for one of the entropy decoding, deblocking filtering, andinverse quantization, or all of the processing. The decoding processingunit for implementing the moving picture decoding method described ineach of embodiments may be shared for the processing to be shared, and adedicated decoding processing unit may be used for processing unique tothat of MPEG-4 AVC.

Furthermore, ex1000 in FIG. 35B shows another example in that processingis partly shared. This example uses a configuration including adedicated decoding processing unit ex1001 that supports the processingunique to an aspect of the present disclosure, a dedicated decodingprocessing unit ex1002 that supports the processing unique to anotherconventional standard, and a decoding processing unit ex1003 thatsupports processing to be shared between the moving picture decodingmethod according to the aspect of the present disclosure and theconventional moving picture decoding method. Here, the dedicateddecoding processing units ex1001 and ex1002 are not necessarilyspecialized for the processing according to the aspect of the presentdisclosure and the processing of the conventional standard,respectively, and may be the ones capable of implementing generalprocessing. Furthermore, the configuration of the present embodiment canbe implemented by the LSI ex500.

As such, reducing the scale of the circuit of an LSI and reducing thecost are possible by sharing the decoding processing unit for theprocessing to be shared between the moving picture decoding methodaccording to the aspect of the present disclosure and the moving picturedecoding method in conformity with the conventional standard.

INDUSTRIAL APPLICABILITY

One or more exemplary embodiments disclosed herein are applicable to atelevision receiver, a digital video recorder, a car navigation system,a cellular phone, a digital camera, a digital video camera, and thelike.

The invention claimed is:
 1. An image decoding method of decoding eachblock among blocks of pictures, the image decoding method comprising:selecting a collocated picture from a plurality of referable referencepictures, the collocated picture being different from a current picturethat includes a current block to be decoded; deriving a candidate formotion vectors of the current block, from a first motion vector of afirst block included in the collocated picture, the first block beinglocated in the collocated picture at (i) a position corresponding to aposition bottom right adjacent to the current block in the currentpicture or (ii) a position corresponding to a position at a center ofthe current block in the current picture; adding the derived candidateto a list of motion vector candidates; selecting, based on an index, onecandidate that includes a second motion vector from the list of motionvector candidates; and decoding the current block using (i) the secondmotion vector included in the selected one candidate and (ii) areference picture of the current block, wherein the deriving includes:determining whether a collocated reference picture of the first block isa long-term reference picture or a short-term reference picture, thecollocated reference picture being a reference picture referred to bythe first block included in the collocated picture; determining whetherthe reference picture of the current block is a long-term referencepicture or a short-term reference picture; deriving the second motionvector so as to be the same as the first motion vector without scalingbased on a temporal distance in the case of determining that (i) thecollocated reference picture of the first block is a long-term referencepicture and (ii) the reference picture of the current block is along-term reference picture; and deriving the second motion vector fromthe first motion vector by scaling based on a temporal distance in thecase of determining that (i) the collocated reference picture of thefirst block is a short-term reference picture and (ii) the referencepicture of the current block is a short-term reference picture, whereinthe scaling is based on a ratio of temporal distance calculated by using(i) a difference between a Picture Order Count (POC) assigned to thecurrent picture and the POC assigned to the reference picture and (ii) adifference between the POC assigned to the collocated picture and thePOC assigned to the collocated reference picture, and wherein the POC isa sequential number assigned for each of the current picture, thereference picture, the collocated picture, and the collocated referencepicture based on display order.